With a lot of clients you'll end up with bogus files on disk as the neighbours of the file you wanted - the client has to download the whole chunk and has to be able to validate its checksum, so it has to put it on disk somewhere. Not a huge problem, but annoying.
Re:The BitTorrent Protocol Specification v2
by daurnimator on Monday August 07, 2017 @11:19PM
(#14953773)
more than a few KB: can be a few MB.
It's especially significant if you have a torrent full of text files, and want a subset.
But can't you already download one file? I suppose if a chunk spans two files, you may get a few extra KB of another file you don't want, but it's not noticeable from a user perspective.