There are two types of open houses you can do when you list your house for sale: a public open and a broker open.
A public open house is what you see most often on TV and that's where the general public can tour properties that are up for sale. The listing agent will set certain days and times that the house will be open, an agent with that listing brokerage will be there supervising, and the public can walk through the house.
A broker open house is an open house strictly for the agent community. Whenever you hear about these broker opens, it's an attempt for the listing agent to get opinions from other agents on price, presentation, and if they have buyers. The general public won't see or be invited to these open houses.
They are two different ways to go about getting traffic through a home. Historically, the public open houses do not sell the houses. Public open houses are mainly used as a way for the listing broker to interact with people that are serious or semi-serious about buying houses and less about selling that particular house. Lately though in 2018, many agents have reported a surge in activity of their opens with several agents successfully selling their listings to buyers from open houses. Go figure.
The challenge with public open houses to a larger degree than the broker open houses is, we don't know as the listing agent who is coming through the house. There is no way currently to vet each prospect that walks through the door. It can also be a safety concern for agents depending on the size and location of the house. You're alone in a house for a few hours in a remote location? Not ideal.
For that reason, our team only does open houses at the owners request and we set expectations that the owners lock away valuables. Depending on the size of the house we would work as multiple agents (2-3) to cover more ground.
Ultimately you will get foot traffic through your home holding an open house. We would dub them ineffective as a whole in actually selling the house.