Sometimes there are no complete copies of a torrent in a swarm, but there are complete copies of individual files. Sometimes the files all rely on each other, while in other cases it still makes sense to want those files because they can be used on their own.

My suggestion is to give greater weight to getting chunks if their whole file is available, since a chunk of a file which is only partially available is usually less useful.

Unless this is already done, in which case never mind

We do not do this, I don't know if we are going to add this, I have bigger things to do at the moment.

Fair enough.

If you do look at this again, one neat thing would be to try to work out the type of the file, because the usefulness of a partial file depends on what type of file it is:

video: still ok so long as most of the file is available
audio: more annoying, but usable
images: probably unusable
text: probably unusable
compressed files: useless