This mainly applies to Generations 1 & 2. In RBY & GSC, the game doesn't actually heal up your Pokémon before entering a Link Battle. Meaning that (again, in vanilla) you could theoretically enter the battle with, say, a pre-poisoned Starmie, which can be hugely advantageous by preventing paralysis & sleep. That being said, in almost all RBY/GSC formats - Ubers, OU, UU, etc. - there exists a Cleric Clause which mandates that all Pokémon start out with full HP/PP/no status.
However, if PS! would implement a feature that allowed you to set starting HP/PP/status conditions for all Pokémon, that would a) allow the Gens 1 & 2 Anything Goes format to be played on PS!, even if it's just in a Custom Battle, and b) allow people to mess around with new potential OMs in any generation. Though Cleric Clause would still be enforced in literally every single ladder format...so not a hugely important thing, but it would be kinda cool I guess.
However, if PS! would implement a feature that allowed you to set starting HP/PP/status conditions for all Pokémon, that would a) allow the Gens 1 & 2 Anything Goes format to be played on PS!, even if it's just in a Custom Battle, and b) allow people to mess around with new potential OMs in any generation. Though Cleric Clause would still be enforced in literally every single ladder format...so not a hugely important thing, but it would be kinda cool I guess.