It would be awkward to smile/pose before/after a funeral, just because I need to call my mum or check my email...

That being said, I do think that there could be a legitimate use case here. One could set up a particular "emotion" (a face pattern) associated with someone forcing them to unlock a phone using their face. I mean, if someone pulls a gun or a knife on me, I'll probably just do as they say and look at the phone, rather than risk an additional hole in my body. But unlocking a phone and sending a distress call is something I could live with.