I am that homeowner. Here are some things I use my tractor for: turn compost (6ft tall piles), till a large garden, grade landscaping for drainage, dig holes for posts and plants, distribute mulch, repair driveway and distribute gravel, and help my neighbors with many of these same items.

I also use it to move heavy items like wooden beams and Mac's mom.

All of this could be done without the tractor, so I wouldn't say it's necessary. My back is not wrecked right now, though, I'm glad I have it. Also, I imagine my use will slow after having lived here for longer (only been a few years so far) - we have several projects we want done at the moment.

The way I figure I could rent a tractor for about $150/day when I need it, or buy an old one for $6k to use for many years and then sell it... probably for near $6k (I know I've spent money on maintenance). Renting every other weekend is annoying, and I often work 1 hour in the evening.

Anyway, hopefully this helps answer your question about why someone with a few acres would own such a thing.