Edit Bar controls: none.
This tool allows you to snap picked points to the nearest point on a 3D bounding box. The snap mode is only allowed if you are currently in a 3D layer.
The cursor is modified to show "Bounding Box" to indicate that the snap mode is active.
The bounding box is displayed around selected objects only and it can be made visible using Visibility - 3D Visibility - Objects - Highlight bounding boxes.
Related topics: Snap Modes and Lock Modifiers.