The anvil
Somepeople say that for going for a walk in the savannah you have to bring with you an anvil. This is because if a lion appears, you can release the anvil and you will be able to run faster.
When I got my glider lincence many years ago, we were told to plan the glide path from down wind to touch down point with the airbrakes halfway out. If you were too short, put them in. If you were too long, put them full out.
So, I think the issue is to operate normaly a little bit penalized in the ratio lift/drag (100%- 102% Nr), but when the things go wrong, in case of a loss of power, you get in a better situation, at least in the lift/drag ratio. This should be around 91% Nr. These are the rpm's that gives you the maximun lift with the minimun drag, because is just what you need in that moment.
This is what I think because I cant prove it.