This is a neat little optimization which can help you avoid needing to convert everything into utf-8 underneath the hood - leaving things in their raw/encoded forms. This may help in certain cases but would probably also make the C-api slightly more complex.

The real problem with Python2 is that it attempts to auto-decode bytes into unicode by guessing the encoding. This actually works most of the time, but not always. Unfortunately the fact that it works at all causes people to ship code that they think is fine... until later when a byte-string comes along with a non-standard encoding and it blows up. Python3 fixed this by making it blow up every time.