But wouldn’t that have to lead to pretty big file-sizes, because unlike Layer Comps Snapshots don’t just save a layer’s position, visibility etc. but a whole different state of the layer’s pixel-content or different layers altogether.
Yes, and No. The size of a single file becomes large, but if I would save each snapshot state as a seperate file (which is the only way to preserve the states at the moment) the sum of the files sizes of those files is definetely larger than the size of a single file, because of all the redundant layers. If you chose to copy the whole layers set of each version and disable unused ones it also adds up more file size and this way you save each state in the same document, too, but without the easy handling of snapshots.
Working with seperate files is a bad crutch, because if I'm playing around with different versions I might have to redo work in each file. (Often I'm experimenting with different colors or placements and sizes). I also don't see the file size as a problem anymore. There is so much space wasted for so many things that I happily use the space for my benefit. The benefit of an option to save snapshots in a document weighs so much more.
Further the snapshot information of an open document is stored in RAM or in temp files on the disc anyway. So the information is already saved. The space will be freed of course if the file is properly closed, but if I need the snapshots for further use I need to save them anyway somewhere.
If I'm experiencing a crash of Photoshop, the OS, or just a power outage all my snapshots are gone. I had serious problems due to the bluetooth bug in the vista drivers that caused a blue screen when you brought your system into or out of stand-bye or hypernation. Unfortunatley stand-bye and hypernation are the only possibilities to not erase the snapshots and be able to continue working on them later. If I didn't save the document in the state of the main version and just played with a suboptimal version my main version was gone (and often I had more than one main version). I had to create seperate files from each snapshot an save them all. Definetely to much to think and care about. Photoshop should make work easier.
Snapshots would make it very easy and straight forward to present different variations of an idea to a client, too.