I just got to the last page of another one of my writing notebooks - that makes 22 of them now.
I've been writing ideas, collecting bits of advice and inspiration, and working out story events and happenings for many years - some years only have 1 or part of a notebook/journal, others have more than one. Sometimes when I read some great writing tips or a new perspective on a writing-related topic, I copy it and paste it in my notebook (with source info). In the past year, I've gone through probably 3 notebooks. I do read over some parts of them, while they are still current, but once they are full and up on my shelf, I don't go back to them very often. But I do think it's useful to look at them sometimes.
Some reasons to look back:
1) Some story ideas seem to resurface again and again, in slightly different ways. Usually when that happens, I know I need to write that story.
2) I like to see how far I've come and how my skill has developed.
3) All the tips and advice that I've collected are like a "mini" writing course.
4) Re-reading the inspirational bits and pieces is a great boost since they seem fresh and interesting again.
5) When I'm stuck or not sure about what direction to take in my writing, looking through my old notebooks reminds me of all the great ideas I had, and often gets me thinking of more.
Do you ever revisit your old notebooks or journals?