Feels very redditty, which is why I'm asking...
Also, what are total buffer size (what does it affect) and session waste (what does it affect)? qbittorrent-nox on Linux.
It can also waste some data when a peer disconnects in the middle of sending a block, causing your client to request the block again from zero. The part of the block that was previously received becomes wasted data.
Additionally, near the end of the download, if a peer is transferring a block really slowly, your client might request it again to a faster peer, causing a bit of waste too.