Definition of Severe Duty, Timing Belts, water pumps and what not

Ok, ok, here’s my question: my (new) mechanic says that they generally change timing belts at 105,000 miles, but sometimes earlier if the vehicle has seen severe duty. The Honda manual states that a truck in severe duty should change the timing belt (and with it I assume the water pumps since you have the guts of the engine all of the shop’s floor for the timing belt job). So what is the definition of severe duty (with trucks…not marriage)? I’ve hauled things…some heavy things across our nation on more than one occasion, but have been timely with maintenance and always speak to my truck lovingly. Gentleman, can you give me a precise definition of severe duty or maybe a functional one? Thanks, hope your well and just to let you know the beer has never tasted the same since I left Boston.