Dude, the fuse is to protect the wire.. The amp has its on fuses and if doesn't, it is recommended that one is put right before, proper sizing. But other wise a 250 amp fuse in 0 gauge WILL blow if there is a short and will keep your power wire from melting and catching fire to your car, regardless how big your alternator or amplifier are, like its supposed to do.
indeed it is...
but also to protect you and your car/instal
for daily use i run double fused... 1 @ front and 1 @ the back cuz i'm running 2 battery's at all times si i've double fused it... just for safe keeps