I think it depends on what truckmount you using- heat ex or propane/diesel burner.
I do make an effort to keep my hours down, by not running the truckmount while vacuuming, setting up hoses, prescrubbing etc..
I know with heat ex models one would be running it more to heat up(right jimmy olas?) He pulles up to a house and the first thing he does he turns on the machine.
I only run my diesel burner truckmount when its being used for cleaning or filling up sprayers.
The other thing I noticed, it gives an impression to my custys that I was quick, by not having to listen to that "loud big machine" out there for too long.
The way I see it I can save sometimes 25-30 minutes on my machine hours on 1 job. It adds up quickly to a couple hundred hours.
With this I used my truckmount for almost exactly 500 hrs since the 1st of january.
My thoughts..