stereoscopic picture of a building being built in Tel Aviv. This is the White City, in these days a world heritage site, being constructed.
When you look at this picture it is obviously damaged. For normal Wikipedia usage, steroscopic pictures are not needed. So only one frame needs to be restored. The second frame however is still valuable as it shows the parts missing in the first frame.. With some clever copy pasting, a reasonable result will be achieved.
Stereoscopic pictures are not needed for Wikipedia, but that does not mean that someone else is not interested in restoring the second frame as well. Saving the restored file in a format that is not compressed ensures that only the second frame needs to be restored. So having the intermediate files is in the interest of Open Content and Open Collaboration.