Pickup Slide is a trick where Link will move extremely slowly while ignoring all collisions other than basic ground checking, and allows Link to travel through most walls as long as there is ground beneath them. Unfortunately because the speed of Link is so slow it can take hours of the game running to just get through a relatively thin gate or wall.
To execute a Pickup Slide Link is required to collect something that has the animation where Link turns around to show the player the item, a common item for this is rupee text, or collecting something from a chest. Link will then slowly go in some direction with extremely slow speed, the angle and speed that Link gets is highly variable and not fully understood yet although angle is based on Link's facing direction and the camera. When talking about variable speed, although it is always miniscule speed over the long period of time it takes to clip through a wall this variation can save a great deal of time.
The reason Pickup Slide works is due to the fact that during the animation of showing the player the item, Link sways back and forth slightly, however there appears to be a missing frame that would otherwise make the animation a perfect loop. Because of this missing frame, every cycle Link moves a miniscule amount in some direction.
There are no applicable usage for Pickup Slide in a speedrun due to the hours it can take to perform the trick, other than low% for theoretical skips. For example Pickup Slide can skip all four poes in Arbiter’s Grounds by bring a pot that contains a blue rupee over to the gate that separates the dungeon, and using the rupee text to skip through the gate. Another use is at the start of Scared Grove being able to clip through the wall that requires Wolf Link to howl at the stone for, you can bonk the tree in the centre of this room for a chance of a blue rupee to fall and use this for the Pickup Slide.
Below are Links to a full non-cut video of using Pickup Slide to clip through the gate in Arbiter's Grounds to skip all the poes, this took around 18 hours but the video(s) are speed up to twice the normal speed of gameplay