My phone (android) doesnt let me use the fingerprint forever - every once in awhile I have to enter the passcode. And on bootup of course I have to enter the passcode. So while my passcode is quite long (and secure) the fingerprint adds a ton of convenience.

I think this is a good compromise - at worst if I were to lose the device and someone were to cut off my finger at best it would only work for a few days. But that scenario seems quite rare.