I jot down music to remind myself how tunes go. I learn tunes by ear fairly easily, but many fiddle tunes and such sound so similar it's easy to get them muddled. Given just a title, I may completely blank on how the tune goes, and even if I have the start, I may blank on how a subsequent section goes. So I keep lists of the tunes I'm learning or have learned, with the start of each section of the tune in ABC (essentially, dots in an ASCII form). Sometimes, I don't even need to decipher the ABC; just the visual appearance of the notation may be enough to make the mental links click.

I also get tunes coming to me at odd times, and if I don't write them down immediately in either standard or ABC notation, they're lost. I can come back to what I've jotted down weeks, months or years later and pick up where I left off. Relying on ear/memory alone, I'd never be able to do this. I've experimented with using a tape recorder for capture, but it's so much easier to file and browse written music--not to mention tolerable.

While a written tune may be just a bare-bones "average" form of how it should actually be performed, I find that if I rely only on memory, I may flake some important and desired aspect of the "original" tune. The "folk process" is not always positive.

Once I've learned a tune from written music, I have no extra difficulty transposing it to a different key.

I've learned so much music from print sources alone, much of which is hard to obtain on recordings--and certainly the cost of doing so would be prohibitive. I generally dislike the pervasive souped-up versions of "trad" music, and often would rather learn the music from untainted print sources. I also run less risk of infringing copyrighted arrangements.

I can't imagine having to learn all poetry from oral transmission alone, without the benefit of print; I can't imagine having to learn (and especially, retain) all music by ear. Written music is such a boon.