Precision maneuvering controls gave starfighter pilots the ability to execute subtle movements in confined areas. In the case of T-65B X-wing spacecraft, these controls would cease to function if the hydraulic lines at the rear of the craft were damaged.
During the Battle of Yavin, Wedge Antilles piloted an X-wing that had poorly-repaired hydraulic lines. He had to abandon his attack run along the trench after TIE fighter fire severed those lines, causing him to lose the ability to make fine adjustments to his flight path.