face recognition: enables you to (mostly) automatic tagging of who’s in the photo
map of images, e.g. look at all the images you have taken in Italy
(local) AI to search images by keywords, e.g. “sunset at the beach”
memories: what happened on this day in the previous years
These are just the ones on top of my head, but you’ll probably get the idea. If you just want to back up you photos then nextcloud is more than enough, but you’d probably enjoy the immich features once you used them.
Regarding the two copies: you can use immich on an external library, so you don’t have to have to copies.
It’s like asking why should I use paperless when I can just keep my documents as PDFs in my nextcloud.
Because it has a lot of photo specific features:
These are just the ones on top of my head, but you’ll probably get the idea. If you just want to back up you photos then nextcloud is more than enough, but you’d probably enjoy the immich features once you used them.
Regarding the two copies: you can use immich on an external library, so you don’t have to have to copies.
It’s like asking why should I use paperless when I can just keep my documents as PDFs in my nextcloud.