I am curious as to why you think people sharing less files is a good idea.
It's a file that is incomplete for years already. I'm tired of uploading it, I think I have a ratio of over 20 for that file. Plenty of people have it, and usually people will download it from me (whatever's available), then realize it's incomplete and delete it - it's a total waste. Everyone who is serious about the file has all of it already, there is no need to upload anymore.
I want to stop it totally, and every few weeks start it up to see if anyone has new pieces. Probably that will never happen, but I have seen it complete a couple of times, but the person never uploads anything. Yes I know this might mean I will miss him.
I have specific files that I keep available for upload, and I want them to use any upload bandwidth available. I set this file to very low priority, but it does still upload eventually.
Reason #2:
If I'm hard linking (rare) files between aMule and a torrent, I need amule to close the file handle so I can replace the part file from under it with a hard link to a different file. I know this is not a common usage pattern. My only other method is to stop aMule, and restart it.
Reason #3:
I have an incomplete file from elsewhere. I want to start a download, stop it, replace the file with the incomplete one and continue. The other option is to copy the data over the file, then do a manual rehash (if that feature is made), or to import the data into the file (if that feature is made). But simply replacing the file uses the least IO.