Overlength can be added to your parts for several reasons. Mostly curved parts need extra material (overlength) to be formed or bend in a machine. The illustrations below show a part that is bend in a press brake machine. The red zones are added overlength.
How to add overlength:
Go to the Overlength setup menu on the top right corner
Select the edge that needs overlength
Tip: Move quickly true the edge selection by using the Tab key
Type overlength in millimeters in the input field
Click 'Apply' to confirm setting
Overlength will be added in the 2D parts (DXF) and is not shown in the 3D editor.