Low CRF values are still handy for extremely minimal lossy encoding. I used CRF 12 for encoding a particularly difficult sequence (720p60) and managed to cut the bitrate by 1/3 (source was ... 100 mbps lagarith?). It was enough bitrate to make sure the picture didn't suffer too much, but there were still some changes because of the inherent complexity of my source.
Either way, we have CRF 0 to 51 to give the luser enough rope to hang himself