to usb or not to usb

[Nemoguitt@aol.com]

my emac has an audio input that i can send signal from my mixer into it and then to PEAK my recording software.....do i need a usb port, what is it's function?.....the usb that i got with my puter has midi in and out which at this point i will not use other than that, it seems i can hook up (2) rca inputs or (2) 1/4' inputs, that's nice but does this justify the expense.....and of course all that will be recorded with this puter are my LOOPS.....:).....michael