It's not just weddings - it's not just portraits - it's every time you send out a flash over a long distance and capture the image with a long lens. Red-eye! If your flash is plugged into the hotshoe of your DSLR you are guaranteeing extra computer time to isolate and correct the problem. Do 500 shots at a dance show and that is 500 x 30 seconds at the least = 4 hours sitting there waiting for the thing to crank over.....arrrrgh.
Answer for me was a Stroboframe Press-T bracket. It puts the flash high enough over the lens axis to illuminate the dancer but NOT fire directly into and off the retina of the eye. No redeye = no computer drudgery.
Their other brackets - the Pro-T or the Folding Flip are equally good. You can hold them up for the entire length of the show and they make sure that the post-processing won't hold you up later.