That's completely different depending upon how large one's yard is, how many obstacles, and how far apart the obstacles are.
In my case, we have 1.5 acres, 14 trees (aside from the Cypress trees that line the far back part of the yard), a 12x16 shed, and children's playset (designed and built by me). We have a 66" deck, zero turn, Swisher, with a 27 hp Briggs & Stratton engine.
All the trees are 16' apart (or more), and most of the cypress trees have grown enough that they require very little cutting underneath of them.
Now, if I had 1/2 acre or less, I wouldn't go with such a wide lawnmower.
If there were a fence that didn't have a wide enough gate opening to fit the mower, I would have bought a smaller deck mower.
The zero turn mower is fantastic to use once I got used to it. I found that I often ended up going over the same spots more than one time because the traditional craftsmen didn't turn quickly enough to work as easily as the zero turn mower.
Edited to add: We bought it for $4,000 with only 120 hours on the motor. And it still works great going into our 3rd year.