No, they are not completely pointless. If I remember correctly I believe the test for the DC-10/MD-11 (can''t remember which) found that the angle of the slide versus the jump the passengers took leaving the door was a definite problem.
The "passenger" generally leaped out of the door instead of dropping onto the slide. This cause the passenger to be catapulted like they had been jumping on a trampoline. If memory serves, a woman broke her leg during the test and they had to modify the angle of the slide to help prevent this from happening.