I mean, just as an example, if you're working on a weird embedded system (so you can't really change compilers) where certain parts that are UB in the spec are

I mean, just as an example, if you're working on a weird embedded system (so you can't really change compilers) where certain parts that are UB in the spec are guaranteed to have certain behavior? Additionally assuming function pointers are the same size as void *, which isn't guaranteed by the spec, when you're working on platform specific code. Although they may start optimizing that one at some point.