Beyond the features that the sibling comment mentioned, this kind of data isn’t really for end users. It’s a way that you can package it up, “anonymize” it, and sell the data to interested parties.
For someone like Notion, they probably aren't selling this data. The primary use case is internally for analysis (eg product usage, business analysis, etc).
It can also be used to train AI models, of course.
That "probably" is doing a lot of heavy lifting. That said, whether they sell it or not, it's all that data that is their primary value store at the moment. They will either go public or sell, eventually. If they go public, it'll likely be similar to Dropbox; a single fairly successful product, but failing attempts to diversify.
"Selling" is a load-bearing word, too. They're probably not literally selling SQL dumps for hard cash. But there are many ways of indirectly selling data, that are almost equivalent to trading database dumps, but indirect enough that the company can say they're not selling data, and be technically correct.
Is that why they’re putting images in Postgres? I don’t understand that design decision yet.
Notion employee here. We don't put images themselves in Postgres- we use s3 to store them. The article is referring to image blocks, which are effectively pointers to the image.
I... Don't think they are? If you look at the URL for images in notion, you can see the S3 hostname.