You'd have firefighters holed up in their stations for weeks at a time with nothing going on. Getting them involved in other types of calls keeps them sharper and more alert in my opinion - even though there is undoubtably a lot more expense involved.
Agreed. It’s good training and makes for a good use of their non fire fighting time. The expense though vs hiring extra paramedics and vehicles I would say using the FD is likely cheaper and a better use of resources long term. Diesels will go on forever. Or rather more miles than they will ever see even in double duty use.
If the FD is rural and not around a big city like San Diego or Atlanta for instance they may have extra time on their hands but all Firefighters are required to maintain equipment, have training, continued education along with house duties.