Like you alluded to, pretty much all the information available in the PubAPI is also exposed on the website in some fashion. Even your openings are aggregated here: https://www.chess.com/stats/openings/{{username}}?daysAgo=90 (although that page may be a paid extension, I'm not sure). Accuracies are exposed in the API if they've already been calculated via Game Review, but other than that, I think a lot of people use the API for clubs and Tournaments. In any case, the real pro of storing your own data is the flexibility of choosing what you want to do with it. You mentioned a dashboard - you can make your own that doesn't have to follow the flow of the Insights page (https://www.chess.com/insights#overview), for example. I made a dashboard as well back before Insights were a thing, but it kind of became obsolete when that feature came out, lol. Nowadays, I use the API primarily to pull PGN data, specifically to process them offline for some fun projects whenever I want to brush up on my coding. Hope this helps!
Extracting Useful Data from the API
Hi there @Mystic1674. You could use the "eco" part of the api, which links to the opening used in any specific game. It takes the form of a url, but you could parse the end of the url and manipulate the data that way. 
This seems to have now been incorporated into the PGN, but still accessible.
This seems to have now been incorporated into the PGN, but still accessible.
I went back and looked at a game from 2023, and the ECO (and ECOUrl) is there in the PGN, so I think it's been accessible for a while now. And the 'eco' API link at the top level response was not present, so that is 'newer' (newer than 2023 at least).
Anyway, the ECO code in the PGN will arguably be way more useful than the link for grouping games, so that would be what I would use.
I'm planning to use the public API to populate a database and build my own dashboard (possibly using Notion, though I haven't decided yet) to track my stats. From what I’ve seen in the documentation so far, the only useful data I think I can get from the API that isn’t already available on the website is the list of openings used in all my games. With that, I could identify which openings I tend to lose the most with and focus on studying them.
Has anyone else tried this? Can anyone think of other useful data to extract from the API?