[throwaway2048]

The point is, certain text, especially shift-JIS and the various EUC encodings can look exactly like an 8 bit "extended ASCII" when its in fact a variable width 8-16bit encoding.

Its bad advice that leads to corruption.

If you already know the encoding, then OP's advice is useless, if you don't but suspect its an 8 bit extended ASCII encoding, it might not be, because the aforementioned look exactly like an 8bit encoding.