For me the main value of ABC lies in the collections of tunes that can be found in this format on-line.

When I first started to deal with tunes and notation it was with a program called Mozart. This was ABC based but I used it as a standard notation editor and didn't actually write ABC files. I still have a collection of .MZ files and after reading this thread today downloaded the one month free trial of Mozart 14 and spent several hours converting my whole collection of .MZ files to abc. It has to be close to twenty years since I stopped using Mozart and there were some pleasant surprises and re-awakened memories.

When I started teaching at a college the program used was Sibelius. I got quite proficient at Sibelius and, in the process, stopped using Mozart. It's a bit strange by todays standards. For example there's no 'File' menu option. There is an alternative but you have to figure it out. The £99 price tag does not compare well with Musescore and over the last few years I have got as used to Musescore as I was to Sibelius.

Mozart, Sibelius, Musescore and ABC. I can produce scores in all of them but now the only two I need are Musescore and ABC. With ABC I can access the fantastic file resources on-line but I can't do guitar tab. With Musescore I can do a score that combines notation and guitar tab. A guitar composition or arrangement works well with notation on top and tab, with aligned bars, below. I find it easiest to notate a piece first and derive the tab from the notation afterwards. However I usually read from the tab because in the tab all the work in figuring out the fingering has been done.