There is a whole range of sharpness levels between dull and "sub micron shavings in one of these Japanese planing contests". The amount of attention paid to the back of a blade is one aspect in this range.
In a plane you get a backside wear bevel that can be a very obvious shining line along the edge. This wear bevel is the result of the shaving gliding over the back of the blade. Do you need to remove it? Well, that depends on the level of sharpness you are shooting for. The shavings allready polished the back of the blade quite a bit. Not Shapton 30 000 grit polish, but still quite good. The shinyness of this line is an indicator that it isn't so bad at all.
When you sharpen the bevel, especially on an oilstone, you get a substantial burr, leaning over to the backside. Pushing the back over the stone bends this burr back to the bevel side again, even without really touching the wear bevel at all. A bit of back and forth between bevel and back side bends the burr enough to weaken it so it breaks off. Then a bit of stropping removes even more remnants of this burr.
I think this is why craftsman of old could get away with a pretty hasty sharpening regime, without ever really touching up the back or even flattening it . They weren't producing the sharpest ever edges with this method, but still good enough for their work. I suppose even back then there were heated debates in the pub on this subject, if they didn't have anything more usefull to discuss.