It doesn't impact the board and there's not even a guarantee that the effect will do anything meaningful
That ability is "when the last defense counter is removed from this permanent, exile it, then you may cast it transformed without paying its mana cost." This means that if for any reason a battle enters the battlefield without defense counters, it will be put into the graveyard and its controller will not get the chance to exile it
Who should pick it: Anyone who values fast stated processing and a simple ordering experience
The same can be said for trainer cards, like Miriam in the Scarlet and Violet base set
Tribute to the World Tree is helpful as well, playing into the +1/+1 counter theme and bolstering the power of the rest of your small creatures
In an Un- game, if X is actually infinite (Urza's Fun House is a pathway to many game states some consider to be unnatural), you can assume that every natural result on a six-sided die is rolled infinite times, leading to infinite Clown Robot tokens and infinite +1/+1 counters on Clown Car