Are you sure?
Take the following example: You are the sole releaser of a file. 20 people download the first chunk, so you decide not to share it anymore. For whatever reason (file completed and taken out of share, just going offline,...) these 20 people disappear.
Compare the perspective:
- You know that 20 people downloaded this chunk from you. You assume, but don't know, that these 20 people will upload this part of the file and stop sharing this part.
- A downloaded get's the available parts. He knows exactly what chunks are currently available and can make a decision to download a chuck based on these facts.
The downloader has better information. And if you lie to him (by hiding chunks), he can't make good decisions anymore. In the worst case, he sees that the file is not 100% available and decides to stop downloading.