Each material comes with quite a number of tweakable technical and pricing parameters, and filling them out for similar materials one parameter at a time may become boring. That's where duplication comes in handy.
Let's say you have set up Black Resin GPBK02 / Black Plastic for your Formlabs Form 2.
You could click "Add New Material" and start with Grey Resin from the top,
, you could also instead click this icon:
This is the result. You can then edit the Black Resin GPBK02 copy / Black Plastic by clicking the edit icon:
Simply change the Material name and the Display name:
and click "Save"
Except for Material Name and Display Name, the two materials are identical, and both are available on the widget: