If you have an annual pass and go to the park during the day, do they let you stay in park (if you have HHN ticket) in holding area while they shoo everyone else out?
Technically you do. There are day tickets for the park and there are night tickets for HHN. If you are in the park and have a HHN ticket instead of leaving when it closes you go to the holding area. That amount of time between when the park closes and HHN opens is Stay and Scream. It also gets you into the houses before the people standing outside waiting for HHN to officially open so it is beneficial to be inside the park before it closes. Since you (in theory)paid twice as much as the people who show up at 6:30pm they give you a few extra perks for your money.