You can't just generalize everything that can possibly happen as 'derping'.
For example, say you're on the cannon closer to your starting spawn, you see an enemy approaching. Since the cannon is closer to your side, the smart thing would be to wait for reinforcements to arrive rather than go out and engage him solo. Here charging up would be 'derping'.
But if the cannon was the opposite cannon, the longer you wait the more likely the other side will have reinforcements coming. Here you want to charge up to the other guy fighting in the middle of nowhere because if you wait, you'll get overwhelmed by their reinforcements.
In a game of Huttball, it's easy to find yourself separated from the main pack with a bunch of reds surrounding you. By keeping them occupied, you delay their reinforcement from catching to your ball handler.
Disengaging from PvP is very hard if the other guy at all knows what he's doing. I often pick off people making a mad dash for an objective and kill them while taking no damage since they're trying to get to the objective. How can whatever they're doing possibly be useful to their team if I killed them before they reached their destination while moving the same direction?
When two people encounter each other in the middle of nowhere, it has to be advantageous for one of the people to engage, and you don't necessarily have to even know who it favorites because if the other guy isn't stupid, he's not going to let you disengage anyway (and if he's disadvantaged you won't let him leave either). Yes very rarely you can disengage with a quick CC or whatever but it's rare. I'm not saying everyone has something great worked out when you see two guys fight in the middle of nowhere, but the cost of disengagement in PvP is usually death, so even if it was a bad move, you don't really got a choice.