To Washer or not to Washer??

Hello,

Wondered if i could get some advice on washers.
Im building a road bike for the first time. Im not clear whether or not to put a flat washer against the carbon forks and then use the kinda spikey one that comes with the caliper. Or just go straight on to carbon with the spikey one.

Ive been looking at bikes in the shops, so do some dont? What do you guys recommend?

Thanks