When you press A, B, Start and Select at the same time, you pull up the Save menu. If you choose to Save+Quit, you will be warped to the last major entrance that you took. A good example of this saving time in a speedrun is at the beginning of the game. If you enter and exit Madam Meow Meow's house and then travel to the beach, you can save and quit as soon as you get the sword in order to save the trek back into town. This eliminates about a minutes worth of travel.