Traditionally, every Magic: The Gathering set has that one or two win condition cards that offer victory by sticking to a certain gameplan. Mirrodin Besieged is such a card in Modern Horizons.
The Phyrexian choice allows players to win automatically by simply putting 15 artifacts into their graveyard. This also guarantees the victory at the end step, which is much better than waiting for the beginning of the next upkeep. So you can basically win the turn you play it.
Lastly, this is not a legendary enchantment, which means that you can play more than one copy with different choices on board.