Brutus seems to finally have made up his mind regarding killing Caesar, so let's bring in some fellow conspirators!
Apart from Brutus, Cassius, Casca, and, to a much lesser extent, Decius Brutus, the conspirators are a fairly nondescript bunch who never really develop individual personalities. However, because their names are repeated out loud several times throughout the play, they somehow give the impression of being more present than they actually are.
Don't get too attached to any of them, is what I'm saying.