Because of the 3up defence and flying
Nope I echo the why here.
It forces the opponent creature to try and hit something it can't, and is difficult to hit for the few things that can. If you have a use for both cards, there's certainly nice synergy, there, but I wouldn't put either card in just because of the other. COR and Guardian Angel is much better all around, and universally useful...
Tataree is a mediocre support card for a mediocre strategy (Samara Tree). Elsewhere in Arena it's just really poor, but it is worth having in Domination.