under certain conditions you might be unable to find which one of the files is wrong, its useful if someone hasnt compressed the mp3's as well
and if you want to verify how many files there should be, or check an incompleted set
plus as youve noticed, its useful for the ftp hosts since they can check alot quicker
it also allows you to see if the host's ftp contains a dammaged file, since the sfv is normally generated by that, and will tell you if its the same file as the one on the ftp (corrupted or otherwise) thats useful because it saves trying to download a dammaged file more than once to find it still doesnt work