Anyone undersize their fuses?

I already did a headlight upgrade to Quadratec LED headlights so should be ok on stock headlight switch. I only had concerns to blow fuses earlier due to adding my own harness addition off the radio connector to run volt gauge, back lighting on said gauge and the backlight on the Quicksilver shifter I am adding and those wires are only 18 to 20 gauge. And seeing a 20 amp fuse just makes me wonder how it needs to be that big for just back up lights and radio which radio is gone but still.