I had the same idea about Notion before, and after using it the best way I have to describe is that it is a database manager, and what can it do is up to you. You can use it for simple note taking (and it does have nice features for that), but also add databases in certain formats, with properties, links between them, run "queries", add reminders... In a sense, it's like coding a (very) basic application without coding. Pretty helpful, for example I use it for managing recipes and shopping lists automatically (among other things).