I usually leave 2 or 3 dollars for the maid.
I leave it on the pillow, sometimes in change. They don't make much. I don't mind.

As for the RoomService delivery charge, it goes to the hotel, not the worker. Room Service workers usually get the short end of the stick. I kid you not.

I enjoy good service, I don't mind to pay for it.

In all,I tip for service, not obligation.