I’ve kept both. Synology photos does auto upload from my+wife’s phones. Then Immich scans this as an external database to import.

Synology keeps the photos in a normal name and folder structure. So the files can be accessed and organised in a normal file browser. Moving to a different device or app is as simple as copying the files over. These folders are backed up off site so even if my hardware dies, I don’t have to set up Immich again before I can access the images as they’re normal image files.

Immich auto upload puts the photos into its own database that is not human readable. I didn’t want that. But I do want the AI tagging, search and fast browsing Immich has. If I didn’t already have Synology photos set up, then I might have tried using Syncthing to send photos to my NAS and then access through Immich.