Question(s)...

1. Does super seeding introduce any inefficiencies into the seeding/downloading process? Like, is it slower? More CPU/RAM used?
2. If not (1), why isn't super seeding on by default? Wouldn't it result in overall healthier torrents?

That's all! Just thought of this question. If a dev sees this deffo chime in. Thanks :)

In super seeding mode you only share torrent pieces that are rare (no other peer have them). It's useful if you have a limited data plan or a slow upload speed, but it's not recommended to use with private trackers unless you don't care about the seeding ratio.

It's a specific choice to be made when you know you need to use limited upload capacity (total or per-torrent) most effectively in presence of many peers. Otherwise it might not be the best option. Therefore, don't press buttons if you don't know what they do.

Super seeding is a misnomer. In Bittorrent the downloading peer decides what pieces to pull. Too often people stupidly use "sequential" download that BREAKS the expected flow and KILLS active torrents, ending up in a situation where no one has the last few pieces (99%). Not a single client until Tixati 2.69 had a safe sequential setting, that would allow sequential while preserving torrents' health.

Under these constraints, all Super Seeding does is HIDE a seeder's downloaded pieces information and only show 1-2-3 extra pieces which the individual downloading peer doesn't have yet. This way it's the seeder who controls which piece is downloaded next.
- this makes sequential downloads impossible by design, because peers can't request pieces they like anymore. It's the worst mode of download when there are few seeders left
- nobody in the swarm knows if there exists a seed with 100%, because you always show 0%+extra pieces to every new downloader
- if all downloaders behaved correctly, they would download rarest pieces they observe first
- Super Seeding turns this on the head, where you offer pieces in a random fashion (not very optimal) or based on peers you as a seed observe -> only good if you are the first ever seed with many downloaders, who are not connected to each other

TLDR: Super Seeding should only be used on initial releases where you are the seed and many people download from you at the beginning.