The video pretty much explains it all.
In case you missed it, last week a huge exploit was found in League of Legends. Using a deceptively simple workaround, it was possible to put more points into a single mastery than the maximum allowed. It sounds like no big deal until you consider that many of them feature cooldown reduction of summoner spells, which led to this video. Watch as the Urgot zips around the battlefield with hundreds of instantaneous flashes, insta-killing Baron and dragon with Smite spam. It has since been fixed, but I think it's worth it just to see this video.