Because all the work I do is with good old stick in the mud 7-bit ascii
files. If random bits of unicode have crept into my files I want to know
about it, and I will if I see lots of octal escapes on the screen (but I
won't if emacs helpfully renders the characters correctly for some
definition of correct :-). For that matter all the files I work with are
Unix format, so if DOS line endings have crept in, I want to know about that
as well by seeing the $#@! ^M characters instead of having them go invisible
on me.