Jacking to change a tire or service brakes or bearings?

I carry two bottle jacks, a 12 ton used with a 10" by 10" block of wood to use on the frame to take most of the weight off of the axles, and a smaller 3 ton (I think) bottle jack that I place under one of the U bolts.
I have had to do that maybe 3 or 4 times in the last 10 years.