Torrents are peer-to-peer (p2p), so anyone is a equal participant. If you download (leech) a file you connect to other user who also have part of the file and upload (seed) it to you.

This means a torrent can only be downloaded if enough users have the file sitting in their torrent client and upload it to others. That is called seeding.

If people download the torrent and don't continue to seed it after finishing the network takes a hit since someone else has to upload that much more. If not enough people seed the speed is either slow or the torrent might die completely if no one who has the complete file seeds the torrent.

So a good torrent user would ideally wait until they uploaded the same amount of data that they downloaded. E.g. they have a 1:1 up/down ratio on the torrent or at least seed it for a few days/weeks.

An open port is important so other people can downlaod from you. A VPN without portforwarding means you most certainly won't seed much since only people with portforwarding themselves can download from you.

tl;dr

Seeder because they allow others to download the file and seed it in return. Leecher because they don't help the network but consume bandwidth.

Streamio only uploads while watching so it's unlikely to come anywhere close to a 1:1 ratio. Real-debrid also doesn't seed after they downloaded the file because that'd cost them bandwidth and thus money.