I think it just dictates the number of poles the motor has? The fewer the poles the less torque it has, but higher RPM. Either way you have to gear it down for EV use, so I suppose it doesn't really matter much in the end, except if it makes the rotor less likely to explode.

I would've expected very high pole counts to be more practical though, since a lower RPM is more manageable in terms of bearings wearing out. On the other hand, steppers have a high pole count and their efficiency is crap so maybe they can get more power out with fewer poles.