iOS recently allows you to unlock apps with faceID.
Some apps on Android give you the option to enable biometric unlock. Unfortunately, not all of them do this. I think this feature should be optional for any app, regardless of whether the app's developer enabled it or not.
I think this feature is greatly beneficial. The attack scenario I am envisioning here is where your phone is stolen while it's unlocked. There are many apps that I use that contain information I'd rather not have exposed to a thief (personal information, including last 4 digits of CC, are accessible in Spotify and Tidal. My calendar contains private info including medical stuff. I also consider my contacts list highly sensitive). I use multiple profiles to mitigate this, but using multiple profiles come with their own convenience costs.