My guess is they want to have a PIN as a short-term credential analogous to the Touch ID, that is, it only works for X hours per password auth before needing password auth again, and then you only get X tries on the PIN before it either locks the PIN out and you need the full password to reactivate it (or I guess it could wipe the laptop à la iPhone).
what im saying is that i dont want to type in a long ass password all the time
and biometrics have "legal problems" as stated above
a pin or allowing touchid to automatically be disabled after a period of time or computer movement ("please enter password to login") would be greatly appreciated