Torrenting requires way more resources than people realize. It's easy to look at your torrents' download speeds and think "oh, that's less than a normal download, like from Steam, so it must not take nearly as many resources" -- it's not all about bandwidth. The amount of encryption and hashing involved in torrenting is fairly CPU heavy (every ~4 MB piece has to be hashed and verified), especially if your CPU doesn't have onboard encryption hardware (think mobile devices). The sheer number of connections involved even in just one torrent can also bog down a network like you wouldn't believe -- anyone who runs a home seedbox can attest.