Figure 3.24 - Merge results
If you want to use a dedicated shortcut for the Merge, you can also
press the M key with vertices selected. That will call a small menu with
Merge options only.
Tip: For the example in Figure 3.24, you can repeat the Merge to
connect the other vertices.
3.6.1 Fixing extrudes with the Merge
One of the uses for the Merge option in Blender is to fix problems
created by the extrude, where you might forget to undo a canceled
extrude during the transformation stage.
The problem appears when you press the E key to extrude and press
the ESC key before finishing the extrude. That cancels the
transformation, but the extrude's new elements will still exist in your
scene.