Why would you not wash your own bike and lubricate it yourself !!!!
Well one reason is that professionals have the right equipment and training to do it properly (you might but not everyone will).
Another reason is too busy.
Another reason is hating cleaning.

We've always have Nooj do our 3 bikes and he will travel from Newbury if there is a days work (3 or 4 bikes).
It's well worth spending the money on IMO.