For the longest time I used to keep all the notebooks I’ve ever used.
At some point after moving it all for the millionth time I sat down and went through it all and threw out 90% of it.
And at a later point, right before moving here I threw out the rest.
The reason I don’t keep them is that I never look at any of it ever. So when I have filled a notebook and have transcribed the content I want I just throw it all out.