It depends on the expected load you think you will be dealing with. I change it for the occasion or use a circuit breaker, but a good short will blow them all! For me the primary purpose of the fuse was to keep from burning up the wire when I shorted it out from being clumsy! 12V is quite impressive when it starts sparking under a dash or in the trunk. Long ago I started to slide a piece of rubber hose over the exposed end so I didn't have to be quite so careful getting things in position to work.