Waypoint
The waypoint's use lies not in itself, but in how it can be used. Navigation upgrades can detect waypoints, so devices with a navigation upgrade can use these waypoints to navigate the world. This is particularly useful for writing easily reusable programs for devices such as robots and drones.
Note that the actual position reported when queried by a navigation upgrade is the block in front of the waypoint (indicated by the particle effects). This way you can place it next to and above a chest, and can refer to the waypoint's position as "above the chest", without having to take the waypoint's rotation into account in your program.
A waypoint has two properties that can be used when querying it via a navigation upgrade: the current level of redstone signal it is receiving, and an editable label. The label is a 32-character long string that can be edited either via a GUI or via the component exposed by the waypoint block. These two properties can then be used on the device to determine what to do with the waypoint. For example, a sorting program can be set to treat all blocks with a high redstone signal as inputs and those with a low signal as outputs.