One of the best, and underused tools in BF3
We usually use it when advancing on an mcom, one set of smoke on the mcom itself and smoke elsewhere covering doorways etc that enemies might be hiding behind.
Also very useful for firing into doorways or areas you know there are enemies, go in with prefire after smoke and you should get them
Also useful for scaring the expletive out of people and getting them to move out of any good cover they have, because they are scared that they are getting assaulted, many of these guys move into the open where they are an easier target