The original Archenemy set captured this nicely: Whether your planeswalker is an old friend, a new ally, or just someone who owes you a favor, they can come to your aid in your battle, and they are willing to cast their spells at your direction to help you defeat your adversary
There is no similar drawback for Vehicles
III You may activate the loyalty abilities of planeswalkers you control twice this turn rather than only once
Even a tiny flaw, like a microscopic print dot or slightly off-center borders, can be the difference between a 9 and a 10
These field guides really remind me of the field guides and nature books I grew up flipping through as a kid (or still do as an adult)
Spells with split second only prevent new spells and activated abilities from going on the stack until those spells resolve, but once the spell with split second resolves, you're free to interact normally with any other spells on the stack