[AHan]

On a planar magnetic diaphragm, what are the advantages of having several thin traces vs. one big trace that takes up the same area?

Basically this vs this (if the second he-6 driver picture is indeed one single trace and not many thin ones)

 

[tangent]

Copper is expensive?

 

[NiHaoMike]

PCBs (including "flex PCBs") are made with a subtractive process, meaning it actually costs less to have more copper left on the board.
 
The main advantage of multiple small wires instead of one big one is flexibility. That's why stranded wire exists. It also conducts high frequencies better than an equal amount of solid copper wire due to the skin effect, but that is not significant in almost all audio applications.

 

[AHan]

The main advantage of multiple small wires instead of one big one is flexibility. That's why stranded wire exists. It also conducts high frequencies better than an equal amount of solid copper wire due to the skin effect, but that is not significant in almost all audio applications.

 
@NiHaoMike I'm pretty sure you're talking about cable here, not traces on a planar magnetic diaphragm, but I could be wrong. If I am wrong, you're saying that several smaller traces etched into say an aluminum covered mylar sheet will make the diaphragm more flexible?

 

[NiHaoMike]

Take a piece of flex PCB that has a section of thick trace and a section of many thin traces. You'll find that the section with many thin traces is much easier to bend.