High Market is far and away the most played card in Commander from Mercadian Masques. It also saw a reprint before in From the Vault Realms. Tends to see play in decks like Kukusho the Evening Star, Starke of Rath, and others that have need of a way to sacrifice at instant speed. Being reprinted in the Plunder the Graves Commander 2015 deck helps get this useful utility land into more hands, as well as bringing down the price tag.
The payoff of sacrificing a creature to gain 1 life is secondary. However, decks that care about gaining life can often find room for it, being a colorless land. Primarily, you use High Market’s effect to sacrifice creatures that you would lose to removal anyway. Also, effects that bring in creatures that would exile them at end of turn don’t always require that the creature be exiled if it’s sacrificed.
One Commander deck that really likes High Market is Zirilan of the Claw. Zirilan’s ability brings a Dragon out of your deck, but that Dragon has to be removed from the game at the next end step. However, you can get around that effect by sacrificing that Dragon with High Market and sending it to the graveyard instead, where you can get it back later.
Kukusho has a powerful effect when he dies so you want to be sure he actually dies and isn’t exiled. Starke of Rath has a powerful ability to destroy a target artifact or creature. However there’s a major downside. Starke then has to be given up to the owner of the destroyed card. If you sacrifice him to a card like high market however, the destruction effect remains in the stack. That means once the effect resolves he’s no longer there to be given up to your opponent.
While you typically can only use High Market’s effect once per turn, it can also provide you with a colorless mana. But, in any deck that likes an extra sacrifice outlet with a small benefit attached to it, this is your card.