Yes. All torrent clients I know, including WebTorrent Desktop, seed while downloading. WebTorrent Desktop keeps seeding after you've finished downloading a file, and keeps running in the system tray after you close the window unless you explicitly tell it to quit.
We want to be good citizens and keep the swarms healthy.
Absolutely. I'm just asking because in certain jurisdictions seeding (illegal content) will lead to huge fines, and not mentioning this on the homepage might lead people to believe that they can safely use this software. This is especially worrying since "streaming" is oftentimes understood as a read-only operation which cannot be pursued by law enforcement.
The general rule of thumb that seems to keep you under the radar is to limit your upload rate. Most clients have an easy option to do this - although apparently this is non-trivial in this client[1]?