Its passive ability, which puts a +1/+1 counter on a creature each time you gain life, is an easy way to combo off with cards like Walking Ballista
To transform it, you just need to pay a small amount of mana
Its not perfect, but if youve got a few Creatures and Enchantments out youre usually going to be popping off
A lot of popular commanders have unique abilities that players build around, turning them into combo pieces or creating a deck that relies on having them in play
(Well, unless you're playing the excellent Fire // Ice, of course.) Aftermath, on the other hand, always gives you that wonderfully useful extra card
The only exceptions are Commander, which is another beast on its own, and Limited formats such as Draft, which has a minimum deck size of 40 cards