I generally don't feel like I have to maximize, and having a pass doesn't stop me from doing other things. I get them for my local park where I expect it to pay off (Cedar Point). We've been so busy this year that it hasn't quite paid off yet. Halloweekends will put me over the top.
The other reason I get them is for pure flexibility. We tend to go on week-long trips to "somewhere". I'll usually get a season pass to a park in the area, and call that our "home base". We can go to that park anytime, without constraint. It's nice to know that, if you have an afternoon free, you can just pop in somewhere.
For example, on our Dells trip, we got season passes to Noah's Ark. My son and I visited one day just to play the mini-golf course there while the girls had gone horseback riding. We still went to Mt. Olympus for a couple of days, rode the ducks, went to Timber Falls---so we did a bunch of other stuff too.
The year before, we got passes to Dollywood and Splash Country in Pigeon Forge. It didn't save us any money---the three day ticket would have been a little bit cheaper, even with parking, etc.---but it was nice to be able to just pop in for the last hour one day, just because we could.
*** Edited 8/28/2008 1:43:58 PM UTC by Brian Noble***
http://www.eecs.umich.edu/~bnoble/