Earnest money is the seller's call. Sometime the realtor will put their 2 cents in, but look at it if you were selling a house. You'd want some kind of commitment (or skin in the game) so that you knew you weren't wasting your time on someone who had no intentions in buying your house.
As an investor, it's dependent. If you're a wholesaler, you probably don't want to have to put earnest money down. My first deal, I sent over a contract and it had no earnest money. If you have a house under contract and want to assign the contract to an end investor, you'd want earnest money to make sure they were committed to closing.
My personal thoughts are what's the harm in earnest money. I always put in an option period so I can back out of a deal in case there are major issues with the house that come up in an inspection. I plan on closing if there isn't so 1000 is no big deal to give the seller a sense of security.
It's dependent on the situation. What's the situation you're referring to?