Is there any strategic reason to skip a turn to untap Time Vault?
One consideration is if there is some symmetrical negative effect in play, such as Smokestack or Bottomless Pit. Skipping your turn skips a trigger on such cards that would effect you.

Another possibility would be if you're able to essentially take your turn during your opponent's turn. Prophet of Kruphix is pretty good for that, as is Seedborn Muse. Of course you're not getting combat steps, but there are plenty of decks which don't need combat in order to win.