They didn't have to worry about over working the horse
They could spend all day ion the field and come back when the work is done. With a horse you couldn't do a whole field at once. They didn't have to do everything by had they could take a little brake from the all the farming and not have to walk behind a horse and sit on a tractor
Helped the farmers
They helped farmers to get done faster and not was spending time in the field plowing or cultivation. They didn't have to was there time do things for there horses like feed them and take care of them.