In the 3D viewport a common operation would be to use the mouse to rotate by left-clicking (or, strictly speaking, left-button-pressing) & dragging. The same sequence is also used for other tasks, though, such as resizing a ROI, or moving a fiducial marker (from the the the Markups module.
It has happened to me occasionally that I have intended to rotate the 3D view, but ended up inadvertently grabbing the handle of a ROI or a fiducial marker. In such cases I’d like to be able to safely disengage the handle without making a change. In other applications a similar action can be accomplished by pressing the
Esc key on the keyboard before the mouse button is released.
Currently it is possible to lock marker positions, but they are unlocked by default, and some users must also like to have the ability to drag the marker positions from time to time. A ROI can be hidden, but sometimes a user will want it to be visible while also rotating the 3D view.
On some other occasions I might have wanted to resize the ROI, but ended up accidentally rotating the 3D view. (Maybe it could happen to some users attempting to drag a marker too.) Likewise in this converse situation it would be helpful to be able to disengage the view rotation safely, without changing it, by pressing the
Esc key before the mouse button is released.
The other option, of course, would be a global
Undo functionality, but I imagine that would be a bigger job.