It doesn't actually save time for the speedrunners who discovered it, but not everything is for higher scoring

Doors, a notorious evil that haunts architects and game developers throughout all of time and space, usually work pretty simply in 1996's seminal 3D platformer, Super Mario 64— all except one, which cannot be opened from the "outside." The one-sided door missing an outside handle at the bottom of Cool, Cool Mountain's slide has bothered Mario 64 enthusiasts for nearly three decades— but finally, a hackless answer has been found to this dilemma.