Raw should be used only under very special circumstances.
It is possible to crash Mathematica by creating a fundamental Mathematica data object with Raw, and specifying illegal internal data for it. If you create an object with head Real, but with internal data incompatible with Mathematica Real numbers, you may end up crashing your whole Mathematica session.
Raw encodes data so that two hexadecimal digits represent one byte. Identical hexstring may lead to different internal data on different computer systems.
You cannot necessarily transport raw arrays of bytes from one type of computer to another without encountering byte swap incompatibilities.