When I select these cards, I try to appeal to the most deck where they could fit as a requirement to make the list, among other criteria I arbitrarily and capriciously decide on
As more and more creatures with enter the battlefield effects, low costed high toughness, or mana taxing abilities have been printed, the one-for-one trade that Lightning Bolt offers has become less and less appealing
At the beginning of your end step, put a +1/+1 counter on each modified creature you control
These are all things that synergize with greens general strategies, so you arent stuck building an elf deck if you want it as your commander
Because you cast whatever creatures Azula swipes, you don't need to worry about giving it back if your opponent removes Azula like you would with Mind Control variants, and the enters ability means your opponents are always two-for-one'd at best