Re: byte-compiler emacs-18 compatibility mode should be removed

[Richard Stallman]

    I was rather wondering why this "backward compatibility feature"
    was introduced in the first place.

To give people a way to compile files with newer Emacs so that they
will still run with older Emacs.

    But what about my other argument which says that incompatibilities
    will show up because of macros, even if the byte-compiler emits
    valid byte codes.

It is true that compilation in the newer Emacs will use the newer macro
definitions.  That could be a problem or it could be a benefit,
depending on the situation.