Is the fuse necessary? if the wire being protected goes into wall, yes for sure. When that wire acts as its own fuse you can have a fire in behind the wall. OTOH a short wire out in the open that melts may not be any worse than what the battery itself does when it "melts."
In cars, the rule is your battery fuse on the wire going to your audio amplifier needs a fuse within 18" of the battery. If the car is in a crash, making the wire to the amplifier in the trunk (say) melt from battery shorting or whatever, they don't want that fire making things even worse. But that 18" of wire at the battery will be its own fuse before it gets to the actual fuse.
1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.