if someone is doing work for you, buy food/snacks for them.
A, because it's nice to not have to stop to find snacks when you're in the zone on a project.
B, because hierarchy is bullshit and it's the least you can do for your subordinates to feed them.
C, because you're paying them and you'll probs get more bang for your buck if they're well fed.
D, because you want to build rapport and improve the odds that they wont try to fuck you over.
E, because it's just a nice thing to do.