if you have no Pokemons on the field at all, you lose the game
As far as I can tell, there's no difference in rewards between the two, it's just a tacit acknowledgement that you're up against opponents who'll probably know their stuff, or not
Life, death, rebirth, and life eternal, Jetmir's cult carried within them the spirit of the family that would become the Cabaretti before the first migration to New Capenna
You also have a smattering of ways to turn life gain into big damage, albeit through creature combat
Other than that it's a decent source of ramp in an enchantment/enchantress deck, especially if you have landfall triggers