Tags vs. notebooks

[pgacv2]

Can someone please help me understand the specific functional differences between tags and notebooks? The Help and user guide don't explain it in much detail, and the screens for both tags and notebooks look similar to me in both the mobile app (iPhone) and the website. I used to use mostly tags, then I started keeping some notebooks, but I don't really know what I should be doing (or can be doing) differently for either one. I'm just using both of them as buckets for highlights and notes, but I'd like to know what's different about each one so I can use them more effectively.

Thanks in advance.