In The LilyPond Report #4, Valentin Villenave writes:
So, what can make you use an old LilyPond version? Is LilyPond
"moving too fast", as suggested on the Download page? (Honestly,
I've always seen that as a purely rhetorical question.)
Is it because of your Linux distribution? Is it a matter of taste?
In my case, it's usually because convert-ly isn't converting something
important. I was on 2.0.6 until the current version was 2.8, because
there was no way to automatically convert lyrics between 2.0 and 2.4.
(I may have the exact numbers wrong.) Yes, the manual change was
pretty easy, but I have hundreds of pieces, each of which has a dozen
or so lilypond files, so doing a manual conversion is not trivial.
Even if you manage to script it on the piece level, it still is a
major time investment to run the script and look at the output.
So the "moving too fast" question is not at all rhetorical. If you're
trying to put together a book, and you have to convert the earlier
pieces several times before you finish transcribing the later pieces,
some people consider that "moving too fast". Or the developers might
consider that the transcribers are "moving too slow".
I consider it unfortunate that lily development seems to live on the
bleeding edge of so many programs. So I currently have a pretty major
project that I can't recompile because I'd have to hand-convert all
the lyrics to run the current version, and I can no longer run the
older version on my relatively current Ubuntu linux system.
The reason I'm currently using 2.10 instead of 2.11, which would
enable me to make more of a contribution to testing current
development, is that I've never managed to convince the developers
that there should be a feature freeze some weeks or months before a
stable release. I got burned badly having to convert lilypond files
from an odd-numbered version before I could use them on a stable
version once, so now all my production work (which is most of my work)
is on stable versions.
I've once thought I didn't like the look of the newer version as well
as the older version, but once I got used to it, I decided I was
wrong. (It was when the lyrics font changed sometime before 2.8.)