I’m replacing a trivial pcb in a battery pack for a small fan. It’s 6V (4xAA) with a SPST top left and a USB socket top right. But why on earth would the power line on the pcb follow that curved path? There are no other components, just the 2 ends of the battery pack and a plastic housing.
Maybe just ‘because you can’?
Yes. And the meandering is probably to make it long and thin, so it trips at a low current. Maybe there's more benefits with consistency and thermal dissipation. PCB trace fuses have the obvious downside to wreck the PCB if tripped but they're for free. (And it makes sense to protect batteries in specific so they don't catch fire, so the placing close to the battery makes sense.)