Silencing shot and arena pvpFollow

As far as i remember my self i was BM..Now i changed into MM.And i want your help to make a guide for silencing shot.The only thing i know is that it stop casters from casting for 3 sec..Does it works only on casters?In other classes is useless?e.x. when a hunter want to use a sting is that consider a casting?

So after these basic informations i would appreciate if anyone good or decent MM pvper can wright some ideas when it would be more apropriate to use silencing shot..like:
Locks=when he tries to use fear
Mage-puroblast,sheep, in general everything..
healers=when they try to heal
sham=
hunters=

etc