On the Harleys I've had the rear brake was only ever used on (a) emergency stop or (b) on a long slowing downhill/slightly loose surface.
Despite the 'Harley brakes are crap' crows I locked up the front on a dry sealed surface when trying to avoid a sheep that ran out on front of me unexpectedly - enough to have smoke coming off the front tyre according to those behind me.
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