Buffering allows the user to prematurely hold a (or any number of, depending on the situation) button, with the action being executed either after an animation occurs or after doing a certain action. Inventory menu buffering is most useful, especially in Link's Awakening DX.
When you open a menu to pause, the game goes through a small animation to open the pause menu. Exiting the menu will cause another small animation will occur. Since there is lag in gaining control of either the pause menu or Link during these animation segments, they are known as pause lag and unpause lag, respectively. What you can do with the various forms of menu buffering depends entirely on which release of the game you are playing on.
In Link's Awakening, holding the A and/or B button(s) during unpause lag can be used to buffer certain items: the sword (see Quick Draw), shield, Pegasus Boots, and Power Bracelet. It is also possible to buffer the save & quit menu - which will cancel out the unpause animation entirely - as well as the Select button. Pause lag allows the user to perform the Despawn Glitch with the Magic Rod, but not Jesus Jumping (which was only introduced in the DX version)
In Link's Awakening DX, holding any number of buttons during unpause lag will cause whatever action is associated with that/those button(s) to happen once the unpause lag ends. This includes the Start button, which means the user can advance the game one frame at a time. This is useful for executing certain frame-perfect tricks, including Dethyl Skip as well as Pit Clipping. Pause lag allows the user to perform Jesus Jumping, but not the Despawn Glitch with the Magic Rod - the new animation patched it out.
The save & quit menu has a fade-in and fade-out unpause and pause animation in both releases of the game. This means Pit Clipping can be done on both versions. The only problem is that the save & quit menu can only buffer the game frame-by-frame in very few cases, and so Pit Clipping is significantly harder in Link's Awakening without the Mushroom. Likewise, the buffering of inputs acts much the same as the inventory menu buffering of whatever release you are playing on.
Note that Jesus Jumping is still impossible to do on Link's Awakening via save & quit buffering, regardless of the fading animations.
The input mechanics of map menu buffering act the same as the start button buffering mechanics of whatever release of the game its being done on. For some reason, the pause lag animation takes four frames after pressing Select to activate, meaning one can easily advance the game by four frames in either version by holding Select during the unpause lag. Map buffering is useful for speeding up the buffering process of certain frame-perfect tricks, including Dethyl Skip.
When transitioning between screens, holding any number of buttons during the transition animation will cause whatever action is associated with that/those button(s) to happen once the animation ends.
Pegasus Boots buffering can be performed by latching on and/or picking up an object (such as grass or rocks) while Link is charging the boots. The next dash he performs will need less time to charge.