Fingerprints are a very feeble form of biometrics. India's, Aadhar - A biometric-based ID system that primarily uses fingerprints is the best case study to understand this. Fingerprints, like every other human organ, are subject to wear and tear, this combined with probabilistic algorithms to find a match for a given set of fingerprints makes it a fragile system for "unique" identification.
It's reasonable for casual biometrics, such as a phone unlock, where the likelihood of someone with a match trying to use your phone is remote. Many people will choose the same password or PIN, for example, but of course you can't change your fingerprint on a whim.
