I use the rear brakes all the time. The balance between the front and rear is a good skill to develop in my view especially with the kinds of loads we tend to stack up on these guys. Good rear break help with heavy braking is needed up front can shorten your stopping distances dramatically.
I also use the rear brake for trail braking in the hills. Not something you read much about but being an old formula racer I learned the value of trail braking on racetracks and it works somewhat on bikes as well. The caviat is obvious I suppose, don't try this at home. But seriously the rear brake , while it can dump you if used abruptly can really be a good tool for helping in the loaded conditions in tight places. If you ever run a police obstackle course you will learn to use the rear brake almost entirely so practicing the rear braking techniques is just another helpful tool in the tool box , in my view. I say this admitting fully to not being an expert at it , more like a student of the art.
"No matter where you go, there you are "
2008 BMW R 1200 RT
2009 DL 650 Wee Strom