I keep everything in case I want to revisit an old project for whatever reason. I don't see any reason not to, since I have plenty of storage space. I have actually loaded an old project or two years later to see what the heck I did (good or bad.) I'm another one who's not really interested in old photos or other memorabilia, but I do keep all my old DAW projects.
 
-Susan

Yes.... If you're just writing and recording for fun, there's really no need to keep anything other than the exported tracks.  Some projects can exceed a gig or more of space.... so deleting makes sense.
 
If you're sending to film and TV libraries and publishers, it's a good idea to hold the original files, archived to a storage drive if need be.  You never know when a library may call and say.... "so and so big wig TV producer likes your song but they don't like the fiddle part... can you give them the song without the fiddle?"  and if you have deleted it, rebuilding the song from scratch may take too long..... especially if the request is "and oh, by the way, we need this tomorrow morning" for inclusion into the tv show or film.
 
Save the projects and save them in such a way they are easy to find again. nothing bites like searching and not being able to find a critical song because you have it under a different name.

These pretty much cover it for me:
 

yorolpal
I keep most of them because I'm almost never actually done with them.

jamesg1213
I keep old projects because I like to open them up and listen to them occasionally, maybe tinker around with the mixes a bit. It's nice to have a record of stuff, and it takes up very little space.

 

BobF
I keep them because they all represent pieces of my own creative effort.

I keep mine because I'm a hoarder.

Guitarhacker
Yes.... If you're just writing and recording for fun, there's really no need to keep anything other than the exported tracks.  Some projects can exceed a gig or more of space.... so deleting makes sense.
 
If you're sending to film and TV libraries and publishers, it's a good idea to hold the original files, archived to a storage drive if need be.  You never know when a library may call and say.... "so and so big wig TV producer likes your song but they don't like the fiddle part... can you give them the song without the fiddle?"  and if you have deleted it, rebuilding the song from scratch may take too long..... especially if the request is "and oh, by the way, we need this tomorrow morning" for inclusion into the tv show or film.
 
Save the projects and save them in such a way they are easy to find again. nothing bites like searching and not being able to find a critical song because you have it under a different name.

This makes sense to me. 

Beagle
Suppose George Jones or Brian Eno called you and said, "well, I'd like to produce your song, but we need some changes in the mix.  can you send me the stems?"
 
Happens to me all the time. 

If Brian calls, Beagle, tell him that Pedro said his music was getting boring and that he misses the Warm Jets and then some!
 
NP: Baby's on Fire!

 
Somebody already mentioned they like to keep track of their musical creativity  …+1 
 
The bulk of my saved songs projects are works in progress . So on the days when life gets tough , I need a good laugh 
 
Kenny

Hi,
 
The way I see it, is ... how to update things so you don't lose the song, since nowadays, technology is changing so fast that pretty soon that LP ain't gonna play anywhere. I would make sure, at least, that you can bring the song up in a new version and a 2nd version, and a final version that is not susceptible to a company that dies and you lose your product.
 
I, now, have ALL of my writing on a computer, and luckily, I started on computers on 1989 and I knew that doing a poem on a typewriter was not effective and too slow a process to help you along the whole thing. The computer, is specially helpful with novels, short stories and the "flow" kind of thinking and writing ... is neat and a breeze with them! It was way harder before, because if you got interrupted, it was hard to pick it up and continue.
 
I have printed and digital copies of my work, btw. But not sure, Have no idea actually, how many of the folks here actually have a staff with their songs on it, for publication purposes, or future possibilities ... I would imagine that is a seriously important part of the work, but maybe I think about this more than it really is.
 
I love the poem I wrote 35 years ago, as much as I do one today, and I marvel at the difference ... I have never looked at it as ... gosh, you were so stupid and such a kid! ... it's how you learned to ride a bike ... so what? Appreciate it ... there is some beauty in there ... some real beauty!

This seems true for me. I found my first recording I did with GTpro on a disc. I even found my song old man joe which was the first song I did in Sonar. They sound funny to me now. It's been a fun ride!