It doesn't have to be formatting...

It is not a "very bad idea" it is "an idea you do not like." Those are different things.

The way you're describing UTF-32, it can't work at all, and it definitely does.

Trying to save space by using UTF-8 over UTF-32 seems like a very small gain to me, is all. UTF-32 is simpler, for text created in that encoding.