Swaki said:
and this may just be me, but i really hate those guys who pick up the sniper in l4d, its more about crowd control than target focusing.
Its a situational weapon and sometimes it can be very effective to have a sniper on the team. of course there are portions of the game when you absolutely don't want a sniper rifle but then each of the weapon types (assault, sniper, shotgun) have their advantages and disadvantages.
Also, in the right circumstances the sniper rifle can be just as good as the other guns at crowd control, or even better because of the massive penetration.
Conditions favourable to using the sniper rifles in L4D:
1) Distance, any map area that is open enough to give you long range shots can benefit from a sniper.
2) Ammo conservation, if you're likely to run out of ammo thats a good reason to take the rifle.
3) choke points, if the zombies have to bunch up and run though a choke point you can scythe them down with the sniper rifle.
Situations not to take the sniper rifle in:
1) hordes coming at you from all sides.
2) indoors or otherwise confined.
3) Tank.
Of course is does somewhat depend on the skill of the sniper too, and the latency he has to the server. there's no point taking a sniper rifle if you can't hit anything.