During the final space battle of Return of the Jedi, Admiral Ackbar says (emphasis mine):
We've got to give those fighters more time. Concentrate all fire on that Super Star Destroyer.
Referring to the Executor.
A series of vessels, including several X-wings and a suicidal A-Wing pilot, then proceed to attack the vessel at point-blank range, taking out is deflector shields and destroying the bridge. The ship then proceeds to lose control and collide with the Death Star, where it is destroyed in a remarkable plume of fire.
My question is how attacking the Executor gave the fighters (led by the Millennium Falcon) more time. These fighters were currently flying through the Death Star's superstructure in an attempt to knock out the main reactor. Other than a few TIE fighters, they were virtually unopposed once they got inside. The Executor, measuring at 19,000 meters long, was far too overwhelmingly huge to pursue the Rebels into the Death Star, and seemed to pose no direct threat to the fighters. So how did focusing their attack on the Executor give the fighters more time?