In the real world, on short sectors, especially in crowded airspace, the "economic" cost profile is not something that any pilot has control over, nor does he have time to be dabbling with such matters...because he is too busy with ATC communications, flying SIDS and STARS or otherwise comply with "unplanned" altitude assignments and vectors, airspeed adjustments for in-trail spacing that are hardly "textbook" profile. For openers, in many instances you don't get your "economic" altitude; you're made to descent early [burn more fuel] or late [with speed brakes], ...saturated ATC traffic flows that make a mess of your optimum planned flight profile.
