I don't tip housekeeping in order to benefit from it - I expect to get the service I am supposed to get automatically (and I do).
I tip them because it is a very low paid job in many countries.
(I also leave my room nice and tidy to make their work easier).
But the remark about tipping everyday because of different staff is a good point - I have considered this but decided to do it only once at the end of my stay - partly because it is easier and partly because I'm not very comfortable with tipping in general and don't want it to seem like I expect to benefit from it.