Do you use them with your dog?
I was told a while back that the dog should be able to respond to only verbal cues and not need the hand signals, so I tried to never even incorporate them during training with Desmond, so neither of us would get in the habit and learn to rely on them.
However, I eventually ended up using signals for a few things (accidentally), especially sit, down, and other basics, as well as snapping my fingers for "focus". He used to suck at laying down, he would kind of dawdle and wouldn't down very quickly, but when we started using hand signals, he reacted differently to the command. Instead of "...euhh... I'll lay down... I guess." we get "DOWN!!"

He looks so enthusiastic now that he knows exactly what I'm asking of him. I've seen that, at least in our case, the dog learns MUCH quicker when I use hand signals instead of just verbal cues. I figure we can phase them out as we train though, so he can lay down simply on cue instead of looking for the signal only.
Thing is, I always avoided hand signals because of the off case scenario where the dog wouldn't see them, such as if he was far away or was in some emergency situation where he should just respond to a verbal cue. This may be totally far-fetched though. Was I misled when I was told that a dog trainer shouldn't use hand signals? What are your thoughts on hand signals and the importance of them?