I've put off this particular command clinic because, thinking back, I couldn't actually remember how I taught Elka "drop it". It's a cue that she certainly knows, and obeys, as I mentioned in this post, when she dropped the remains of a turkey sandwich she'd found in the park. If I was already eating a turkey sandwich and told to spit it out, I don't know that I would. So, good Elka, really!
So, "drop it" is important. It can keep your socks hole-free, keep a game of tug civil and controlled, protect your fingers while playing fetch, and keep your dog from consuming hazardous things like rocks and bottle caps and the like.