Disclaimer: I only play Momir on Magic Online, not Arena

If you play a land every turn and discrad another one to activate the emblem, you use 2 cards of your hand per turn. But you only draw one each turn. This means that you end up with 6 lands (on the play, on the draw 7) in play when you start your turn with an empty hand. If you play the land then, you have no card left to discard for the ability. If you skip an emblem activation (or two), you end up in a late game with more lands in play. Playing an 8-drop every turn is better than a 6-drop. Also, those skipped one- and two-drops become irrelevant often very quickly.

I alternate between activating the emblem every turn or building up to something bigger. Kinda depends on what my opponent is doing.

Pretty good article here: https://www.hipstersofthecoast.com/2023/06/mtg-arena-midweek-magic-guide-momir/

I haven't gotten there, yet, but I'm trying to get to a 10-drop.

Most 1, 2, and 3 drops are quickly outscaled in Momir, you want to get to making 5+ drops because those are the ones that will win games. So skipping your early turns ensures you have enough cards to keep making 7 drops late into the game.

If you play a land and use the emblem to discard every turn, you can run out of cards eventually, and the 7-drops in the Momir pool (for example) mostly provide better value than, say, the 1-drops. At least that used to be the case when the decks only had lands. Now the decks have some non-land cards, and if some of them help you draw (can't remember which cards are in there), maybe it doesn't make as much sense to pass early.