Given that it is a multiplayer format, it's imperative that your land drops are consistent, and it helps if you can accumulate mana more quickly than your opponents
While this effect was designed at a time in which mana burn was still a rule of Magic, causing unspent mana to deal damage to its owner, but now it's quite helpful for those looking to access political bargaining chips in the midst of Commander games
Promo cards can include special cards from Disney events, tournament and Set Championship promo cards, and other promotional cards for things like gift sets and more
These function like spells attached to lands in that they give you a way to use your mana, mitigating the effect of flood since you can do something, and helping ease mana screw because you can slip in a few extra lands
Theres also a one-two punch where you cast this card on turn 1 and ramp on turn 2