I've had so many situations where my crucial characters survived an attack they otherwise wouldn't have, thanks to that extra durability
On the sapphire side, cards such as Winnie the Pooh, Having a Think will help you to build up your inkwell quickly, giving you more resources to play cards on your turn
Stone of Erech Stone of Erech is a decent egg that gives an asymmetrical Rest in Peace effect to all colors for one mana
No, its not getting banned, because its only vaguely reminiscent of Coalition Victory (which is enjoying a great deal of discussion at the moment)
It was a slow process getting the investment ready and digging far enough into the game to have the cards to spare but if a deck had no use for excess mana this was still a highly effective endgame especially for decks that used Thawing Glaciers
You can flicker it, bounce it, recur it, and more