I never gave it much thought as to saving web sized LOs. Once they are posted I don't see a need for them but I still back them up and I still have many in my files on computer. I save all my files to flash drives and CD's--especially the important things like the kits I've bought and my pictures. I guess I need to do the same with my regular sized LOs as I have been really slack in that area.
I save all 3. I find it particularly useful to save the small web image as I post to multiple galleries and can also use it if I want to email it to a friend or family member to preview. I have moved all of my scrapbooking files to a large EHD so they don't clutter up my computer. I have them backed up on another computer and another EHD. (Backups are HUGE at my house!)
I save them all... mainly because the file managers do not show me the thumbnails of the .psd files.. so I rely on the .jpgs to know which file I'm looking for LOL. Make sense? Besides with 3T of space.. I'm hardly running short at the moment. That could change... lol
I keep the *.PSD files (so I can edit later If PSD goes out of format I'll convert the format at that time).
I also save a *.Tiff file that goes into my screen saver folder (this is my album, because I don't print anymore)
Then finally I have a folder titled WEB that I save the *.jpg file to upload. Every couple months I go back and delete these.
I prefer the larger tiff files rather than jpg, because all my old scrapbook pages are puny and look like sh*t when you try to stretch the jpg to get a good view of the page. With TB harddrives at $100 I just buy another hard drive.