So I ran into this interesting article about iOS and issues the users and developers should be aware of when using Touch ID for authentication. The reason I think this is important to think about, is that it is a design issue, not actually a security flaw.
The point in this case, is that iOS is designed as a single-user system. This is not a knock against the OS, but it is an important point to note, as it isn’t necessarily something everyone realizes. Basically, every registered finger is considered to be your finger; there is no way to distinguish between users who might need different access.
This contrasts with most other operating systems, such as Android, Windows and Linux (even Mac OS X), where each user is separate. It is a use case issue, and not necessarily a wrong one, but one to be aware of.
What this really means though is you need to be aware of the environment you are using, and how the design of that environment may impact the security of your system.