I find the insurance angle a bit hard to swallow about not registering garage journeys in service.
Yes, an operator's insurance would to some extent be proportionate to the number of miles operated, but i can't see that much difference with one more journey a day.
Some operators tend to register their dead workings (even at either end of a council contracted service) on the basis that they need to run anyway and they may as well be open to occasionally getting a few fares. If you include them as part of the same registration when you start the service, there's no additional service registration cost, and at one time you used to get fuel duty rebate on 'service' journeys but not garage journeys run 'not in service' (although i'm a bit out of date on BSOG or whatever it's called this week.)
Although the added time / mileage involved in running in service / running to or from a bus station terminus rather than going straight to / from depot has got to be paid for, and it may not be considered worth it for the sake of a fare paid once every few weeks. And the time might just push the driver's duty over a 'drivers hours' limit.
In London of course it's different, as TFL don't want odd 'when working' journeys happening that will change (and therefore generate complaints about their removal) if a route moves to a different garage either at re-tender or if the operator has a re-shuffle between garages.
If an operator (or driver acting on their own initiative) charged a fare to carry someone on a non-registered garage journey, that of course would be dodgy...
