(1) securing the boom over the side of the boat to haul in a MOB (i.e., with a Lifesling; and (2) securing the boom when the main is down (i.e., if you don't have a boom gallows, etc.) in big seas, etc.

Admittedly, (1) would be a pretty rare use for a boom brake...but they seem like nice pieces of gear for coastal/offshore sailing for various reasons (like, um, easing accidental jibes...).

Had a big squall that changed directions on us, as it bounced off high rock walls, this summer in Glacier Bay, AK Had the boom prevented, and I sure wish we'd had an easier way to un-do it when the wind 'shifted'...fuck, that kinda sucked ;-)

Squall before the wind 'changed directions'...coming down Tarr Inlet. Exhilerating sail...for a while... ;-)