Although it can't prevent combat damage that would be dealt to your planeswalkers, it can still prevent noncombat damage that your opponent would want to redirect from you to one of your planeswalkers
Incarnation Elementals The cycle of incarnation elementals is one of the strongest showcases of powerful enters triggers in Magic
attached to your leader, all of your characters will receive a point to their cost, making it a bit harder for decks like Rob Lucci to remove from the board
A handful of the best ways are Virtue of Loyalty, Chivalric Alliance, Forth Eorlingas!, Court of Embereth, and History of Benalia
if you assume, on average, you're drafting 31 playables for your deck (23 spells, 5 lands, 3 sideboard cards) then approximately 10% of your cube could potentially be strong sideboard cards and the resulting decks would be 'more powerful' than a cube with no sideboard cards
It was largely designed to make mulligans less painful in Standard and Limited
