Came across this on this very informative explanation all about spoilers and speed brakes on a 737.
He describes three different applications, but take special note of the third and last application. Makes a lot of sense now it has been pointed out.
https://www.youtube.com/watch?v=nunCXKIYYyQ
[youtube]http://www.youtube.com/watch?v=nunCXKIYYyQ[/youtube]
His other stuff on the tube is also very interesting and worth a look.
Jan