I also hire then leave them to it quite a lot... recently though I have found that when I come back I have to "finish off" as they have not done all the harvesting/plowing. I wouldn't mind so much if it was in places where trees or other stuff are but it is not, it's random patches all over the place and doesn't really warrant hiring someone else to finish off.
I usually only hire one person for each farm so it's not because they might of thought another person was going to do it!!
