Mana Seism why would I sacrifice lands if I can tap them for mana anyway magic

[Dude]

why would you use Mana Seism if you can tap lands for mana anyway?

[Arix]

Because that way you can do both - tap your lands for mana, then sacrifice them for extra mana.

[Dude]

But then u won't have them for next turn

[Arix]

Nope.

[Josh]

sometimes speed is more important; if you can get something out quickly you can dominate the battlefield;

like for example if you have a powerful card costing 8 mana that could win you the game; with Mana seism you could be able to cast it as soon as turn 5