A kick takes roughly a minute, that would have left approx two minutes on the clock left to play.
If they miss the kick Wales kick long and England who were struggling to gain any dominance are back in their defensive zone under the pump chasing a game with a pumped up Welsh defence coming forward.
If they'd got it, same scenario except not chasing a game.
Kick to the corner and score gives England a minute to wind down the clock on the kick, and means Wales must score a try in a minute after surrendering possession.
The call was fine, the poor call was going to two in the lineout instead of tail where launchbury would have jumped against Tipuric and Wyn-Jones would have been lifting and not Maul defending, or chasing a breakdown - that would have been Lawes (to go to 2) call iirc.