Does it affect the completion percentage, or give an achievement or something? Seems pointleess, but I get them anyways because speed running levels is fun. --- I'm just dickin aroouunnnd SHAKE AND BAKE!
My guess is they set a goal for you to encourage you to speed run. Once you A+ it, you feel more comfortable trying to shave off time. If there wasn't a goal time set, then you may feel too overwhelmed to challenge leader-board times, thus never reentering after completion. --- GameFAQs, where there's an opinion... there's a fight. Never argue with an idiot. They drag you down to their level then beat you with experience.