As someone who does lots of torrent fun, I can tell you that people typically want to throttle their upload speed because ISPs generally give you a lot less upload bandwidth, compared to download. (For example, on some servers, I can often download near 1500k - 2000k a second, sustained, but my upspeed is capped around 50k.) If I leave my upstream unthrottled, playing online games or surfing becomes much slower, especially if I have multiple torrents going, so I usually chop it up in to pieces.