The more features you have on your amp, the more important it is to have a solid control system set up. That's just simple logic, and for plenty of the most popular amplifiers, it's something you can take care of with multi-use amp footswitches. There's no need to constantly be fiddling with channels and effects on your amp when you've got one of these onstage with you - just a quick tap from your toe, and you'll be ready to go. If there's anything that belongs next to your main pedalboard, it's one of the controllers found in this section.
Since there are so many different amplifiers out there, you'll want to take care that you're choosing an amp footswitch that's nicely matched to your own. As an example, if you use Line 6 amps like the Spider IV or Spider Valve MKII, some great footswitches to look at are their own Shortboard and Longboard models. More often than not, amp manufacturers design their switches to deliver the best feature support to their own amplifiers, so that's a point to keep in mind when you're picking one out of the lineup.
Something else you ought to think about is how much you really need your footswitch to do for you. That may seem like a no-brainer, but the truth is that it's easy to get caught up in the bells & whistles and wind up with more controller than you need. For instance, you might consider the Roland FC-300 or Rocktron MIDI MATE if you're planning on integrating some MIDI cues in your setup - but these would be overkill if all you need is a simple toggle, in which case a simple switch like the Livewire LWS21 or Fender 1-Button Vintage Style Footswitch would work just fine.
To sum it all up, your number one priority when picking out a multi-use amp footswitch is simply to make sure it's got the right features for your amplifier and playing style. Whether that means a simple one-button switch or a more multi-purpose model like the Peavey Sanpera is up to you. Either way, a footswitch is a great step toward making your amp setup even more versatile than it already is.