What is the problem with "\relative"? (Was: Do we really offer the future?)

[Gilles]

Yet another subject ;-)

> [...]
> Yet another reason to deprecate \relative, which I now avoid like the
> plague. (Unfortunately, I was suckered into using it when I started
> using Lilypond over a decade ago, so all my legacy code is in
> \relative mode. Using Frescobaldi, I’m slowly converting all my old
> code to absolute mode.)

Why?

Thanks,
Gilles