it all depends on what kind of sequencing you are going/want to be doing. If you want pads, synths, some analog sounds that are most likely going to be packaged in the core sounds of a workstation, it is a piece of cake.
if you to use samples you create, as well as live voices, harmonies, and more custom sounds, its a little extra.
for instance, i use a Motif workstation. its my band's 5th, 6th, 7th, 8th through 16th member. simple, and I route a click to my drummer and a mix of he wants, and we just play along. you have to be well rehearsed, mind you, since if you "fall off" the sequence, chances are your song is poo from that point on.
sampling your own sounds can also be done in these keyboard workstaions, but they are not nearly as easy as software synths.
I imagine one day soon ill be hauling my Powerbook on stage with an external mixer and routing an entire orchestra of sequence from abelton or something, or using it to drive the motif......which is also hooked up to my micro Korg..............which is driving a Dr. Sample..................................
man. it will drive you nuts having so many options. but, its a GOOD nuts.