"How much does it affect *me*"? Depends.

My DSL maximum upload speed appears to be around 20-30KB/s. I don't allow unlimited upload slots to avoid having 200 users all downloading at 10 bytes a second. Instead, I limit to just 2 uploads at once.

Frequently, I'll see people trying to download a very large file at 1K/s. Perhaps, as you say, they are getting the file from multiple sources, but wouldn't it be faster to get it from two or three users at 20KB/s than 10 at < 1KB/s? (the number of sources on any download is limited to a max of about 8 or so).

As for "affecting me", if someone like you is allowing an unlimited number of upload slots, then it might take me forever to download something from you because your bandwidth is stretched to the breaking point.