I generally play FPS games where camping is not rewarded. Standing still will only get you killed, and sniping is, while powerful, isn't usually the optimal course of action.
For example, there might be a few advantageous positions on the map that might work better for a long-range weapon to hit other key positions, but you need to leave your sniping position or else you lose the game. Like, in Quake Live, you can sit and camp all you want, but your armor and health slowly tick down from 200/200 to 100/100, about 1 each second. Armor respawns in 25 seconds (red, yellow, green, shard = +100/+50/+25/+5), and the Megahealth (+100) respawns in 35. If you want to win a duel, you will be attempting to control the armor and health on the map so your opponent cannot get it.
If you sit in a good sniping position, they can stay on the other end of the map, stock up on armor while your armor slowly decays, and eventually they will have a larger health/armor stack and be able to rush your position while you have less effective health than them.
Same thing in UT without the armor decay. But they'll eventually get the same 200/200 you have and ALSO grab the damage amp (90 second respawn I think? been a while since I did a UT2K4 duel). So if you're dicking around waiting for them to come, an intelligent player will get EVERYTHING they possibly can, and THEN come and mop the floor with you because you don't have the resources they have.
That said, if you aim incredibly well and dodge incredibly well, it doesn't matter if they have everything. You can negate their stack with a couple well-placed shots. However, if they are equally skilled as you, two of their shots will kill you instead of taking your armor down a bit.
~~~~~~~~~~~~~~~~~~
However, in a FFA or public game, people are terrible so you can just sit and camp and spam nades and probably win.