If quick copy is enabled in the Mouse pane of the Utilities>Global Options dialog box, dragging with the middle mouse button over some text inserts that text at the previous caret position.

This feature has some additional behavior you might not expect:

It can be used to transfer text between edit panes in a split view.
Holding down Shift while clicking the middle mouse button immediately duplicates all text between the caret position and the clicked location.
If there already is a selection when you start middle-dragging, the selection will be replaced with the region you marked with the mouse.
Holding down Control while dragging the middle mouse button marks a rectangular area, and pastes it vertically at the caret location (or into the current selection).