We've only held WDW Annual Passes twice, maybe 3 times, since making WDW a fairly regular pattern over the past 20+ years. In those rare years, we've maximized the number of trips and are in the parks every day except for departure day. That said, most of our WDW trips are for a business conference and unless we already had an active AP, we have zero park days during those visits.
For vacation purposes, our trips are shorter (~4 nights) and we generally plan to be in the parks "every full day minus 1." So if if trip is four nights, that gives 3 full days ... two of which will be in the parks and the remaining day will be a down day to sleep in, relax at the pool, visit the spa or whatever else the traveling group considers 'pampering.' For this coming trip, we have 4 nights -- but only 1 day remaining on old Park Hopper passes from 2002. So, we'll do only one park day this visit: AK for daytime, Epcot for evening. Done.
@DisneyRegulars, I don't know that we will ever get used to the "use our three fast passes and leave" mentality. I'm well aware of that level of expectation and have grumbled against it many times. I'm so used to 8-11 great rides in a single day from my old-school DLR days ... I simply can't accept "3 rides and done". Nope, I'm not ready to reset my personal expectations ... yet. ;-)