In your developing turns, the flash on it offers you an amazing level of flexibility, letting you waste your opponents mana by not letting them use removal on your turn, catching your opponent off-guard sometimes (especially if they dont realise youre on Mono-Blue), and letting you hold up countermagic whilst still threatening to develop your battlefield if you dont need to counter something
Let me give you a simple example
The ideal scenario would be blocking for a partner, getting hit directly, and ultimately ending up around 2 HP (5 or less if you have endurance)
These are the rarest cards that can be pulled from packs and products, with a very low pull rate
Battles on the other hand have a one-shot effect, and even assuming you are able to cast them transformed on the same turn, they typically present a threat that is more likely to be something most decks are equipped to deal with
1 Foil-Etched Legendary card + 99 nonfoil cards