Allegretto, this is a trick question. Really, only add reverb if your heart desires it. Its a musical choice, just remember that all reverb presets are Not created equal.

I have many different flavors to choose from, but I use none of them unless there is a musical reason to have it in a mix. I still like the sound of most Lexicon boxes more than the built in plugins of today. Sure, the plugin is easy to use but the quality is usually missing. Most of it comes from how the reverb is programed and how the tails respond.

In nature your ear wants to hear a delay before the reverberation starts, in programing this is called a pre delay. The tail of the reverb is how the ear picks out the quality, just as if you were in a canyon and listening as you yell.

Your going to have to do a bit of research on your own with the tools you have to figure out what sounds musical to you given the application. Its really just as simple as that, and be very careful about how much is in your mix, I've found that its really easy to use too much.

Best wishes in your musical space voyage!