Originally, I thought Casual Mode was pointless since Awakening was easy enough even on Hard Mode. I'm experienced enough to how Fire Emblem works (especially since I've played 6-13) and I find it pretty simple. Some games don't come easy to people like Fire Emblem does to me, so I totally understand the inclusion of this feature.
However, I think they should include something like a drawback to balance this a bit. Maybe another character has to leave the map with the character that retreated to make sure they safely make it out. If I remember, FE7 did something similar with Pent and Louise where if one "dies" then the other will leave as well. If they keep the Pair-up Feature, then the character in the back with them will escort them off the battlefield. I don't know, just something to think about.