There is something to be said for working from a base, where you have all your stuff and a stock of spares.
But some of the mobile guys seem to make money too. But as even the Dyson service chaps find, you cant carry everything you might need in a van and are not equipped to do certain stuff like clean DC07 cyclones. Why most don't.
I never worked mobile, but I imagine its quite frustrating to find yourself needing a part that isn't on your van and then having to go back.