How effective can sniping be when people are constantly moving across the map? Your team would have to stop them at an objective just to get the chance to snipe but they will run around and kill the sniper anway........
Should be really effective on attack/defend maps. Defense knows that the enemy is going to be coming to a certain point, and can wait at the end of common paths, as well as cover the objective. Kinda hard to get the objective done if a sniper can pop out from cover and pop the guy in the head whenever he tried to plant the bomb, hack the terminal, repair the bot, etc.
Attacking can also use sniping tactics to great effect, by picking off campers. Stationary targets are quite easy to hit in the head, especially when you know where they are hiding, but they don't know what direction you will fire from. For example, I can hardly think of a better tool for getting rid of the players using the machine gun nests.