We get the avocados mashed and then gently stir in whatever else we're adding (lemon juice + salt if we're going simple, hot fresh salsa + jalapenos + garlic + lime juice + salt if we're feeling fancy).
It's also the best tool for making egg salad, randomly enough.
I mean, I'm not saying you need to run out and buy one if you don't already have one. A fork will stand in for either one of these tasks. But if you do have one lingering around in your drawers, you might want to consider giving it a little bit of extra work.