The FF needs to be left on, sniper claymores are not suposed to be used as base defense or have any type of offensive ability, they are specifically for keeping people from sneaking up on the sniper (e.g. Top of ladders, around corners, in door ways etc..)
The AT mines.. the fact that FF exists is the reason I don't play engineer otherwise I would play that class all day long and put mines down. If you take FF off, you probably won't even be able to drive a vehicle and die to anything but mines.
FF = On
Newbies = Off
Thx.