Earnest money doesn't just secure the home, it does other things too.
First, it's the money the seller can take should the contract provide it and the buyer defaults on the contract. I won't get into that here, but it's considered liquidated damages. In general, you want enough earnest money in the deal so that the seller would rather take the earnest money than take you to court. Luxury homes are a bigger target for litigation that others.
Earnest Money also says a lot about you as the buyer. Low earnest money says, "I don't have any money," or "I'm not serious about this home" or "I'm an investor" or "I really don't have my act together." Whereas high earnest money might be surprisingly silent. For example, putting a lot of earnest money down, so 20% might wow the seller, but it doesn't help negotiations enough to warrant risking that amount of money.
Earnest money is your skin in the game and it is indeed a game. How you play your earnest money could effect the way the seller treats you on other terms. For example, in some cases lower earnest money might cause the seller to be more strict about deadlines like due diligence period and financial contingencies. While a larger amount might afford you more days. In addition, should something go wrong, it's a bit counter intuitive but more earnest money might actually "buy" you more days of trying to work something out, while lower earnest money might get a deal terminated quickly!