The more folders you make the more work it is to maintain the folder structure. I prefer to sort videos according to the combined quality of the actual movie and the picture or sound, which probably the same as the watching experience. Once, my hard disks are full, I don't have to think too long about what to delete and I just can delete the stuff I like least. At the beginning I had folder for each season, which turned out to be also more work without any real value. Now, I just have the main series folder, which contains all the episodes.