There are multiple reasons to do so: re-using when you play this Pokmon on your Bench Abilities, healing a damaged Pokmon, saving an easy target (like Lumineon V) from a potential KO, or just managing Bench space
For example, in Sealed Deck, you should keep a six-land six-card hand after a mulligan, so long as you have all of your colors
At only two mana, Investigators Journal is easy to play on curve, but a lot of the time youre going to want to hold it back until it can come into play with a suitable amount of sus counters
Loyalty counters are affected by proliferate, so this is super helpful if you're going for gold and want to use that -9 ability
This leaves your opponent's board empty and your own battlefield full of beefy monsters you can hopefully leverage to win the game