I save them primarily because things that don't get written up in actual journal entries get mentioned there. I said not very many things about my actual life in my actual journal, back in 1996. wibbble thinks I'm cryptic now; I'm relatively plain as compared to then. He said something about his eye icons; I said that yes, indeed, to the point where the thing with the thing and the nail polish worked.
Had this been 1996, I would have said something along the lines of, "the thing similar to the thing where the thing with the birds happened", that, of course, being a literary reference sufficiently obscure that only someone who had been monitoring my reading habits would know the source literature, and only someone familiar with my logic process and strongest associations would see the similarity.
For example, my DeVry login password can be figured out by a four-hop Loony-logic process, from the keywords "mica" and "magician". Four hops to each, mind, and one's a checksum as well.
Far easier for me to just post chat logs on private, so I can look back and remember what I actually said about my internal states, rather than what I coded.
I've taken to putting a brief description of each interaction in the subject, to save myself time when scanning through the subjects in month view. Recent examples include: iroshi likes Dagger's snark. sithjawa is easily distracted. [F2M friend] is now a man.
I amuse myself.