The speed you are referring to is the minimal fuel flow per unit of time.
The drag at this speed will not be optimum (greater than minimum) - and hence the fuel flow per unit of distance covered will not be optimal.
Think of a car analogy - if you want to travel the furthest possible on a tank of fuel you want to be in top gear and at motorway speeds. A single tank will get you say 700km, and at an average speed of 120km/h will last you just short of 6 hours. In congested city traffic (doing 30km/h on average) the same tank may only allow you to do 300km, which nonethelsss equates to 10 hours of driving.
Golf-Sierra
Last edited by Golf-Sierra; 29th Jun 2011 at 10:57.
Reason: corrected an error pointed out by a subsequent poster