I got annoyed with Immich and external storage, because in order for every user to have their own facial recognition data on a large set of photos, you have to add the folder as external storage for each user, which means image previews for each user, even though the source image is the same. So if you have 3 users, you use up 3 times the space for the same thumbnail image.

It got to where I had 20% of my space was just thumbnails for each user, even though it was one set of images in the external storage.

Maybe that's changed recently.