Its ability to transform into an aggressive saga that creates board presence for you, buffs your creatures, and then wipes your opponents boards before returning to the battlefield with Norns anti-attackers effect is great at keeping your foes from overextending
The rate is reasonable and then you get an attack boost to your entire board for four turns in a row
Your opponents will not be able to cast a single spell when both are on the board
Earlier this year, Ira Glass talked about how hard it is to start out in any creative endeavor, and while alteration is a bit different, a lot of it still applies: Nobody tells this to people who are beginners
Lots of impact, good offense, and reasonable defense
Cards like Archfiends Vessel and See the Truth suggest that casting spells and reanimating creatures from the graveyard will be possible, but those might be Constructed plants rather than intended for Limited