Yeah, that's exactly it. It's an open source alternative to Instagram based on ActivityPub, like Mastodon and Lemmy. In terms of functionality I think it's better than Instagram. There are no ads or sinister algorithms; I can select and copy text; I can easily reshare posts I like; and I can include working hyperlinks in my posts and replies.

The main benefits to running your own instance are that you don't have to rely on anyone else to keep the site running and you can decide for yourself about federating or not with other instances. For me it's also just a fun little DIY project to set up and maintain my own server.