I think it evolved from an informal get-together after the actual rehearsal. The groom's family generally organizes it. IMHO, and I could be wrong, is that it kind of balances who does what in the whole process since the bride's family pays for the wedding itself this is part of the groom's family contribution.

>Just about one of the weirdest things I can't get my head round about the USA is the concept of wedding rehearsal dinners. It keeps cropping up on TV shows and films ("Killer Instinct", "Friends" just 2 exs that spring to mind). Now let me get this straight: Not only do the bride and groom need to rehearse the wedding ceremony - natural and sensible and practised over here - but all the wedding guests get together a day or 2 before the event and rehearse the actual wedding meal, food, speeches and all? So everyone's already heard the best man's amusing anecdotes, the groom's praise of his new wife, the father's musings on his daughter's youth, etc.? And the expanse of it!
>
>Have I got this straight?