"We have new routing, advise ready to copy" are not words a pilot wants to hear from an air traffic controller. Of course, the most efficient route is to fly direct from airport to airport in a straight line. This is rarely the case, as there are often departure or arrival routes that must be flown (SIDs and STARs, respectively). Also, ATC often requires you to fly on airways - these are a series of navigation aids or GPS waypoints that create pathways (highways) in the sky. Again, not efficient, but required. The route in the adjacent screenshot is a real reroute I've been given twice in the past 3 years from Dallas Love to Houston Hobby. A 220 mile flight (42 minutes) turned into a 660 mile flight (hour and 42 minutes) - taking us almost all the way to Midland then down to San Antonio. The first time was to circumvent a line of thunderstorms that were in the way, and the second (the one shown) was because of the heavy traffic flow into Houston (after a series of thunderstorms delayed flights for hours). This could easily trigger the clause in most charter contracts where the operator can charge extra for "unforeseen additional flight time." There is a workaround: you could simply delay the departure if the pilot feels a more direct route could open up in the near future. Works sometimes, anyway.