I used to sometimes write down dreams, or I would occasionally keep a diary when I was going through rough times. That was mostly just to document so that if I looked back I could see how I was improving, but really I feel most of the time I don't have any reason to keep one, so it was sporadic when I tried.
If I have anything worthy of writing in a diary, I just as soon tell someone about it, be it good or bad, rather than keeping it to myself and writing it? Like, if I have a problem with someone I'll tell that person, if I love someone, I'll tell that person, if I had a good day I'll talk about it, if I had a bad day I'll vent a bit and then move on. I don't see the point of really documenting everything. Hmm..