I suppose strictly speaking, but considering the impetus for the inventor of the Jake brake was losing the brakes on Cajon, I think it is safe to say that safety was the driving force in Jake brakes
I can see how a company driver who is governed would want to have the jakes on. Some mega companies like Stevens Transport will call their drivers if they are going about 5 mph past their governed speed on a downhill. If you don’t have this problem, then it’s more fuel efficient to let the truck coast on downhills. If your jakes are on, they will activate once your speed goes over your set cruise control, therefore, defeating the fuel burned to move forward. Braking unnecessarily also costs you money. Now, if you drive at 70 or higher, then having your jakes on is probably not a bad idea.
Depends on where the switch is located and if the clutch deactivates them by pushing it slightly.. I like having them on but only if it’s easy to shut off quickly if needed AKA road conditions change quickly around a curve and it’s icy now.
Using jakes will affect your fuel economy. It won't increase fuel consumption while being used, but it will decrease mileage due to slowing down faster.
Running your engine brake all the time in general is a bad lazy habit, Noob's think shifting fast is a good idea, but these things are not Mustangs, there trucks. They are designed for transporting heavy loads not drag racings. Engine brakes are for the purpose of maintaining speed more than stopping a truck. It should only be turned on when in use. As a O/O you will find in the long run driving with it on all the time can cause transmission problems, and also degrade the quality of up and down shifting. Just opinion.
I’d rather spend my Saturdays drinking beer then adjusting/doing brakes, mine stays on when slowing down but I don’t use it upshifting
My jakes are on pretty much 100% of the time except in truck stops and shippers/receivers. Why? Jakes are free., brakes are not. Mine are muffled anyway so nobody cares.
