Mana Vault offers a huge burst of colourless mana early in the game, helping power out big spells or set up combos. Commander decks that like fast, explosive openings, especially artifact and combo shells, make heavy use of it. The untap cost is often trivial compared to the tempo advantage it provides when used carefully. Its role as a piece of high-octane fast mana keeps it popular in higher-power and artifact-centric metas.