From SmashWiki, the Super Smash Bros. wiki
Screen Adjust is an option in Super Smash Bros. allowing the player align the image from their Nintendo 64 on the television they are currently using. Screen Adjust displays a cross that stretches across four surrounding rectangles enclosed inside of each other. The player is instructed to adjust the middle of the cross into the center of the screen the best they can through use of the control stick. Pressing the Z button resets the cross back to its initial position.
As emulators like Project 64 can automatically center the display for many games, inputs on Screen Adjust in such emulators will generally have no effect.