What the purpose of a diode in parallel with a power switch
Is the circuit of reputable origin?

I am fairly certain it is due to someone seeing two similar things:


A flyback diode anti-parallel to an inductive load
RC snubbers or TVS diodes in parallel with a switch


and then trying to combine them the two (probably due to convenience of connecting across switch rather than the motor or motor driver) without truly understanding what is going on.

Either that or they thought "inductive loads arc and get a diode across them and the switch also arcs when it opens" and it was more convenient to connect across the switch so that's what they did, mistaking the source for the symptom.

It also doesn't make sense because it's not just a motor, but a complete BLDC circuit which already contains measures to deal with flyback.