The Aruch HaShulchan has an opinion on whether one person can motzi (exempt) a crowd with a bracha acharona (after-bracha) on mezonot foods. It is along the lines of it is better not to have one person do this for everyone else. I saw it once, and now cannot find it. I have since heard it is "famous"! Does any one have a source?
And thus is the halachah and the widespread custom that one does not discharge another's obligation in any [brachah], and each makes his own brachah, since even for "Hamotzi" and birkas ha-mazon, there are few in our time [who follow the practice of] one being motzi another, and all the more so for other things.
He goes on to cover be-di-avad cases.