When you are testing your board for the first time if you don't have a current limited power supply you run the risk of smoking tracks if something is not right. A good trick is to connect a lamp in series. You want one that normally draws 3 or 4 times the current you require.
The lamp filament resistance is very low when cold but if you have a short it heats up and goes high resistance protecting the circuit, far quicker than a fuse will blow. A bright lamp idicates you have a problem.
I think the polyswitch may be designed to do the same thing, perhaps someone can tell us what the normal current draw is.
Roy

Thanks Raz, I would hate to think someone might connect it direct to the bike battery, a 5 -10 Watt lamp in series would be ok. I will set my bench power supply to ~100mA then.
Roy