Does not some races have inherent advantages to being a certain class? Then again, maybe that was just a feature of the shadowrun returns pc game. Anyways, for me it would depend on the setting and the lore. Like say I would not allow a undead character to be a paladin or a cleric, or Something along these lines. I would also perhaps give bonus to races that would logically be better at certain classes, like say giving the hippie connection with nature elf an bonus to being a druid or something like that. But Keep in mind I never GM'd before, this is just what I would do if I were to.