Box controllers are used for animating parts of the character that are not affected by physics.
Box Controller elements of a character rig (shown with the silhouette of the character)
Box controllers are visible in the Box Controller mode, which can be enabled by pressing the button on the Toolbar. Small details of a character model, like fingers and parts of the clothing, are convenient to adjust in this mode. Aside from this, box controllers are rarely used for editing character poses, as Point Controllers are better suited for this task.
Fixing Box Controllers
If you try to fix selected box controllers at their positions (this can be done by pressing the R key), point controllers corresponding to them will become fixed.
To learn more about fixing controllers, see the dedicated chapter.
An example of using Box Controller mode to position character fingers
The example above utilizes Tail Mode to make adjusting fingers more convenient.