Another advantage of using oACS.
As your site grows you may want to add fuctionality and ACS has a lot already 90% ready to go.
For instance:
Survey: for doing polls like "What is your favorite food to carbo load?" or things much more complex.
Calendar: List upcoming events. If you want to divide events by region and by type consider waiting for Version 4.5 it has excellent group support in calendar.
Event registration: Let people sign up for events online.
Eccomerce: Pay for events by credit card, buy jock straps with your sites logo on it.
SubSites: Allow clubs to control thier own subsites. (This is supported better in V4.5 but doable to some extent in 3x.)
I wouldn't go so far as to say ACS gives you these for "free" but most of the heavy lifting is done for you.
