Nothing wrong with rolling up an NPC. The problems start when you decide you need 23 separate rolls to create an NPC, including randomly choosing their Disposition, Intellect, Materialism, Energy, Honesty, Thrift, Morals, Piety, and so on. Because then you could end up with a modest, cheerful, jealous, anti-intellectual, slothful, lusty, craven spendthrift.