[sudobash1]

I use it for the same reason, but also it is worlds ahead of Musescore if you want to put together a songbook (particularly if you also have tex experience). The best advice Musescore has for making a songbook with many scores is to use a PDF editor on the output.

Also as a programmer, Lilypond is programmable, and nearly infinitely customizable (similar to tex). I love that I can write some style information in a "header" and include it in every score. In my current project I am writing a lot of SATB choral songs in book format. But I also want to do a melody only edition. Just tweaking a header file, I can hide all the other voices, no problem.

(I also use Musescore, which I prefer for composition or simple projects. But when I want to output a large finished product, I always go back to Lilypond.)