Here’s the reason you need to close all of your fireplace screens.  This security video shows some people hanging out in their living room when a burning log rolls out of the fireplace, through the flimsy mesh curtain, and onto their hardwood floor.

The fireplace screen would’ve stopped it, but it was sitting useless off to the left and the fireplace was wide open.  Luckily, a guy was sitting right there, and he rolled the burning log back with his bare hands, then swept the embers back into the fire.