It makes sense to create a definition copy for an existing object if a new object is to have properties similar to those of the source object. Using a definition copy is convenient because you do not have to enter identical attribute values for multiple objects of the same type.
Procedure (quick video)
The definition copy is created. A definition copy is also created when you copy an object to the clipboard (tab bar Start > Copy) and use the Paste function to add it to a diagram (tab bar Start > Paste (Down arrow) > Definition copy).