Advantage? - possibly. If you connect up to a stereo recorder, PA or headphones, what you will hear is the guitar in the centre plus a pseudo-stereo reverb. If you use just the "left/mono" output, you get a mono signal, i.e. a sum of the internal left and right channels. When there is a plug in the "right" output jack, it breaks the right channel feed to the summing resistors, so in that case you get the right channel in the "right" output jack and just the left channel in the "left/mono" output jack.

What pedal?

You need to decide if you want to hear stereo effects or mono.
If you do mono and then later change to stereo, be careful to check all your sound patches to be sure there isn't left/right unbalance. Panning errors can't be detected in mono.
Live on a big stage, many engineers prefer a mono signal but otherwise your sound will feel small in mono compare to a stereo signal with large reverb and delays with different timing on the left and right channels..
I prefer stereo guitar sounds that lets some space in the middle for the vocal bass and other instruments.
Although if you want to record layers (multi recording of the same partition) you may want to go mono and pan each tracks differently at mix time.

Colin, post: 456498, member: 47940 wrote: So I just bought an effects pedal for my Bass guitar".....

Unless it's for an occasional rare effect, bass guitar is usually best left mono, and pretty much panned center, whether on a recording, or live through a PA. Not sure what effect it is, but bass players do like to use a few different things, like a bit of chorus, or something. Compressors are popular, but that need not be stereo, at all. Reverb on a bass could get ugly and smear everything. Maybe a stereo ping-pong delay using short notes for that rare stereo bass effect.

Stereo effects are normally for time-based effects, like reverb, delay, chorus, phaser and flanger, etc. No need for a stereo bass distortion box. You'd just be feeding the same exact signal to two channels, using up two channels of a mixer or two tracks of a recording. Stereoizing bass can get messy.

Bass is (normally) the foundation of a song, along with a nice, solid kick drum, placed center, usually. That gives all the other higher-pitched instruments the rest of the soundfield, left-to-right, to be placed. Different combinations of instruments may be placed anywhere from hard left or right, to just left or right of center. Any instrument, like possibly something on a keyboard whose notes can dive down into bass territory, may be better placed out of the same space as the bass, or even say, a piano that is mic'ed (or sampled) in stereo, starting bass notes left to higher notes going more right. The piano bass notes are STILL going to be mingled in with a mono bass guitar (since the bass guitar would be coming out both speakers, equally), starting on the left, but moving rightward as higher notes are played. A lot of making that work is choice of composition for the bass and the piano, plus careful mixing levels, especially any place two low notes might collide.

The point is, stereo can mainly be used to keep a lot of each others' instruments out of each others' way in a mix. Two guitars often get panned opposite because they are pretty much in the same frequency range, and panning them opposite makes it easier to distinguish between the two.

Back to "stereo bass guitar". If you start stereoizing any mono instrument, the main reason to do so is with time-based effects. Left-right-left-right-left-right. Using reverb can thin out the bass, and muddy it, at the same time. MAYBE a BIT of chorus, but panned BARELY left-right, so it still sticks pretty much to the center, giving all the other instruments room? Almost all (with the exception of low keyboard notes) of the other instruments and vocals are floating around ABOVE the bass notes, out of the way. Putting a low-note kick drum center with the bass, and mixing it in, creates the foundation. Since a snare drum is higher pitched than those, it can also go center (or nearly) and not conflict. Same with a lead vocal, or maybe a lead guitar or other instrument. They occupy the same space, stereo-wise, but not the same frequencies, so they are out of each others' way. Then, you start painting the picture, left and right, with other stuff. The tom drums roll left-to-right in frequency, mimic'ing their placement. Place the cymbals differently, crash 1 right, ride somewhere near center, crash 2 left? (Since the ride normally takes the place of the hi-hat, while drumming, MAYBE just a bit panned opposite each other, but both close to the snare drum?) The hi-hat and ride can be placed near center because they are not in the same frequency-range of the bass.

OK, think about this, also: A bass guitar in mono is using the full power of both channels of a stereo amp, and feeding both low-frequency speakers equally. (Most live stuff, like in bars, is basically mono, anyway, so live...stereo bass is rarely used). THAT is the foundation on which all other instruments are built, and a solid foundation is good. Start messing with panning effects on the foundation (bass), and you start creating problems. Use a delay, and the first note will come out the left, then the right. For that time where only the first note is, you are only using one speaker, and half the total power. THEN, it kicks in on the repeat, the opposite side. If it's a held note, the original will start dying before the repeat. If the repeat is quick, you have just hit a note, using half the power and speaker capability, and then the other half SUDDENLY jumps in. You have the foundation being jittery.

About the only thing a delay on bass might be good for is a RARE well-timed ping-pong for effect, but that would get old, quickly.

As far as an effects pedal for bass, time-based stereo effects can cause problems, such as the "phase" problems mentioned in another reply. IF, on the other hand, a pedal had a "Dry Out" as well as an "Effects Out", THAT might be really handy. Then, you could use any effect, but take the dry out to one channel of a mixer (or one track of a recording), and the effects to another, and then mix in the effects UNDER the dry main signal. I dunno, there may even be boxes that can do a wet/dry mix internally, and output to one jack, having been internally mixed "in parallel" so you could just use one channel of a mixer, say live, and just kick it in for if you wanted a bit of distortion riding below your main solid bass? Personally, I'd still avoid reverbs and delays.

Of course, you could always just use an A/B/Y box, and any ol' effect, and two channels (or two recording tracks) to do the same thing.

Sooooo...BASS GUITAR is very tricky to use any kind of 'stereo effects' on, if what we mean by 'stereo' from one instrument as being 'time-based effects'. It can cause a LOT of problems. If it's not 'time-based', then there's really little need to run a bass guitar in stereo. If it's not actually "time-based", but processing the incoming signal to have one jack go out "dry" and the other "wet", then THAT may be useful, but normally both mixed and panned center, anyway.

Always exceptions to everything, though. I just saw this was about your BASS guitar, and nobody else seemed to catch it, so I just thought I'd throw in some stuff to consider. Nothing wrong with experimenting, though. May be just the thing for some off-the-wall ambo-trance, or something? There are general rules, and then there is "any rule can be broken", in music. What I wrote was just some of the things to be aware of, considering you asking about stereo BASS GUITAR effects.

In closing, someone else already asked, and it is always helpful to know to get more relevant responses...WHAT pedal is it?

Kapt.Krunch