When is aback bevel desirable? 1)If you have a badly dished backside to an ancient iron you want to put to work. 2)If you have a single iron woodie bedded at 45° and you want to play around with higher pitches.
Just in case Eric was not clear, NO back bevel on a chisel. Be fanatically religious about this. It only takes a microscopic bit of bevel in the back of a chisel to ruin its function. It'll still cut, buy you'll have no control. I know this from experience.
I don't but a back bevel on plane blades, because by the time I heard of it, all my plane blades had been flattened & polished, so no point. It didn't take long to get them that way.