When using the file explorer local images have a thumbnail but those on a NAS don't. It's also not possible to, for instance, upload a file from a NAS directly to the internet and some programs (eg. TeXstudio) fail when opening a file from a NAS.
Also when opening an image from a NAS it loads extremely slowly while it's instant on my Windows machine. This loading time got better with an update a while back so now it could be down to the image viewer not using the thumbnail first before loading the full image (this, however, could be related to the issue above).