I'll always wear a suit to a wedding or formal charity event, assuming they are not black tie (in which case the tuxedo comes out), to a job interview or to a formal business meeting.
I'll sometimes wear a suit to the office when I don't have to (law firm, so even though it is business casual, having a suit on isn't extremely unusual), to a less formal cocktail party, to church, or to some networking happy hours. A blazer and greys works nicely for the latter three situations as well.
I don't recommend wearing a suit to a dive bar, most nightclubs, a barbeque or any event that is supposed to be casual. Absent exceptions for advanced players which are beyond the scope of my response, I also don't recommend wearing a suit if you are not wearing a tie.