I think it's just the preferences of the client and provider.  I know for myself it really doesn't matter, really whatever is convienient and comfortable for the gentleman.  Sometimes a traveling businessman does not have access to a car so I am happy to go to them, or on a cold winter night they might not want to leave their nice cozy home or hotel.  xoxo

Some prefer one over the other, some will do both, some will not. No question like the one you are asking has a simple either/or answer.