I normally go for a week at a time, 7 nights, and will usually buy 5 day one-park tickets.
Since I usually drive, I generally arrive for check-in around 8 pm, and that becomes an early night to be ready for the next day. Also, my "leave day" I try to be on the road by 8 am, so arrival and leave days are not park days. With 7 night stays, that leaves 6 park days.
I am a rope-drop-to-close, so I like having a couple of days that I can recuperate. It also allows me to decide to NOT to go to a park if the weather is looking really bad. I will plan parks for every day I am there, knowing that I will not go on at least 1 day.
But that is just me. I am on the school calendars, so can only really travel during spring break and summer, so there are longer hours and hotter weather, but also more people. I enjoy taking a break in the afternoon, but not by going back to the resort but by eating a really late lunch and simply taking my time over it. That saves me travel time back and forth, lets me sit in a temperature controlled environment, and I can use the time to plan the evening.