Curious questions

Apologies for being naive or insensitive I'm just curious. So I am undergoing IUI as I'm using donor sperm, but I see a lot of people posting on here who are either having IUI in a couple, I just wondered why this is the case? Is it due to the fact the sperm get directly inserted this increasing the chances or .... ? I'm just wondering because from what I'm told the chances of IUI working are 10-20% which is the same as natural conception. I could be mixed up though.