It's a dual-use enchantment. You can use it to hold onto a high-level land, like you said, but you can also put it on an opponent's high-level land that you can't take (yet). It also works nicely with Exile.
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It can also be useful to protect a critter with an ability you really want to keep on the table (IE Borgess's boost or an idol), particularly against an invade-heavy opponent.
=^..^=
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I agree with Pez. I use it as a way to protect idols or creatures with TA's that I need. These idols or creatures would be way too risky to level up and land protection wouldn't work because they can just easily be invaded. Peace is also great for slapping on an opponents' high level land that you can't defeat in battle.
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Peace also works great in land transfer decks. They allow you to safely level (for the most part) for the purpose of using Tokebi to sweep it up for great profit.
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