Seamless runs formed on site
Formed on the drive to the exact length of each elevation, so a whole elevation carries no joint at all except where it turns an angle or feeds a drop. Pre-cut sectional stock introduces a join roughly every three paces, and joins are what eventually weep.
Hangers at proper spacing
Close enough that the run holds its line under the weight of a winter's water and ice. Wide spacing is invisible on the day and shows up as a sag and a standing puddle within two seasons.
Outlets where the water actually is
Enough downspouts for the area served, positioned at the low points, and discharging far enough from the wall that the ground takes it away rather than returning it to the footing.
Fall you can measure
A consistent slope toward each outlet, checked with a level rather than by eye, so the run empties instead of holding water between storms.