So I just played against an Intentional Feeder...
...and to be honest, it really wasn't that fun at all. He was just giving my team kills everywhere and I just decided to ignore him after a while so I wouldn't get super fed. He essentially wasted my teams time by giving us a free win. His excuse was that one of his teammate banned his Yasuo and it was Normals and while the guy that banned his Yasuo was being toxic, that is not a good excuse to intentionally feed. So TL; DR: If you intentionally feed, you are not just ruining the game for your team but for the enemy team as well.