It seems cool, but really doesn't mean much in practice. They were all like "YEAH you and all your friends are gonna be in a league, constantly competing against one another and it'll be AWESOME" but really one or two friends in the same league (and not usually the same tier) is all it ends up being.
So then I said to myself "oh it would be cool if I played with the people in my league the most frequently." I had always liked how higher level streamers all knew each other and recognized a lot of players. It would be really cool to be able to be like "oh its AbiwonKenabi again. Watch out for her Nami" and consistently compete and work together with the same group of people. That level of familiarity could be fun, make us feel like pros. It doesn't have to be every game: just enough to where we start to recognize people in our own league. Alas, this isn't the case.
Instead, all it really turns out to be is an arbitrary way to organize players further. No one asks you what specific league you are in ("Are you in Nasus's Urfriders?"), they only care about your league rank ("Are you in Gold IV?") and couldn't care less about Nasus's Urfriders.
Also, does anyone else not care for the names? Some of them are so random. I didn't make Nasus's Urfriders up, that's a real thing. Also, Alitstar's Tricksters. Why would Alistar have Tricksters? Some are ok (Corki's Scouts, Karthus's Blightlords) but a lot are just weird.