There's a difference between farm tractors and utility tractors, although there are certainly areas where they overlap. For the most part, using the machine for tillage, (plows, discs, some tillers) tends to require bigger, higher HP tractors. There are "crossovers", just as there are in the automotive arena.
In the example that Spinnerbait gave, hooking a three bottom plow to a compact utility tractor, even with 4 wheel drive, would probably do about as much good as a Banty rooster out there scratching around....
