There's a good reason to do this if you can't be certain what reserved subnets are used in a given network and you absolutely need a static ip for some reason.

At least that's the conclusion I've arrived at at some point, but I don't remember what was the exact use case anymore.

However there are still several global IPv4 ranges that are not local reserved ranges but are effectively reserved and you could use them if you really want to without any issues.