Question about edges

[Philippe Hurbain]

Generally they are placed on surface edges. Possible exception is when they are used as decoration. Though this is not a very good practice, I have commited this a few times, such as the grip on the latch of NXT cover, or to simulate the complex surface on back of Power Functions XL motor. It has been used also to mark the separation between parts on assembly, where separated parts should have been used.