It would be nice to improve mp3tag with and option to resize artworks to a size specified in some options (W x H). Also user should be able manually select the compression quality (like when saving a picture in Adobe PhotoShop).
Why? There are many artworks are in sizes 1400x1400 and even more bigger + filesize is more than 1MB (like this one). It's OK, I like good quality but when adding such a big artwork to an mp3 file, on many portable audio players the file opens slower than with smaller cover. Also the size of the mp3 increases dramatically.
Of course you can use third party tools but that's a waste of time.