Another thing about public transportation (shuttles from hotels, for instance) to the parks is the timing. Yes, I know edie mentioned "the right time" but I'll also elaborate on that. I read a trip report where someone was staying a a hotel very close to Universal/IOA and it took over half an hour to get to the park anyway.
But, a car can also work as another type of advantage. The parking is covered and you can bring a small cooler with sandwiches and sodas and leave them in the car, and just go out there to get your lunch or dinner...saves money...my parents and I do it all the time.

And since the parking isn't too far of a walk, it's nice.
But I have never tried going on a shuttle, myself, but some hotels have VERY limited times. I stayed at the AmeriSuites and they only had 3 or 4 times for THE ENTIRE DAY. There was one that was at park opening exactly (meaning you'd get to the park at least 20 minutes late...or later, depending if there were other stops or something) and then the last shuttle was BEFORE the parks closed! Could you imagine???

The Fairfield Inn had better shuttle times though...more choices and everything...and the Fairfield was nearly the same location as the AmeriSuites, maybe a block or two farther away...
So, basically, you limit yourself by relying on shuttles. Maybe Hard Rock Cafe, or Margaritaville, or some clubs or a movie entice you after a day at the parks...nice to have the option to go, wouldn't it?
