In the spring you have a specific number of weeks to prep and plant. The amount of food you can produce is directly tied to the horsepower you can apply. It's also the difference between spending 15 hours a day in the field versus 8.
Yeah, I know, more power means you can process a bigger swath of the field faster with one pass. But I've driven a ~15hp tractor, and it could still do a lot more than you'd think.