In addition to all the good points made about what the test chaps do during certification flights is the line pilot’s understanding of several things: energy on short final (mass and speed); touchdown distance down the runway; the importance of quickly getting all the weight on the wheels; seat position relative to the controls (particularly, to the brake pedals); the position of feet on those brake pedals at touchdown; just how far those brake pedals have to be depressed to approach a max braking effect … and, in inclement weather, the necessity of getting all operating engines into maximum and symmetrical reverse thrust. Test pilots are used to all of this as a “day-in and day-out” routine. Typical line pilots are not.
Some time ago we had a discussion of feet position on the rudder pedals during takeoff – but it’s even more important here, because you’re going to land at some point after each takeoff, while (we all hope) you aren’t necessarily going to reject every takeoff. How many times have you seen the pilot, when asked to “set the parking brake,” have to adjust either the seat or his/her position in that seat in order to depress the brake pedals far enough to engage the parking brake? That is at least as far as those pedals will have to be depressed to get close to maximum energy braking. If your feet aren’t positioned to get the maximum mechanical advantage, you won’t get maximum pedal deflection – unless you regularly bench press a small car with your feet. And the seat position is important in the event you have to maintain directional control aerodynamically with the rudder WHILE depressing the brake pedals to their maximum extent!