In the pandemonium example, you can return the creature to your hand, cast pandemonium, and replay that creature all on the same turn.
So you do not miss out on any damage.
It costs 2
but you gain 1 card advantage (because your creature did not die).
Suppose someone antimatters your dragon:
* Reverse time: Cast one your own creature: -1 card (reverse time), -1 draw (your reversed creature) = -2 card advantage + quantum cost of the creature + 1
cost
* Return: Cast on your own creature: No card disadvantage, no quantum cost for the creature (you get a refund when using return), 1
cost
Imagine another situation: You and your opponent both have pulverizer. Whoever plays this weapon first can destroy the other weapon (assume no steal or other PC).
If he/she plays first, then you can no longer play pulverizer. Unless you use return on that pulverizer and then play yours. Now your opponent has to decide whether or not to play his/her weapon (knowing that you can destroy it on your turn while she/he has to wait before using it).