The Point of Fuses

The purpose of a fuse or circuit breaker is always to protect the wire, and it needs to be a close as possible to the electrical source. In the marine trade, ABYC is very specific about this required distance for both shore power and DC power sources and it varies with whether or not the wire is in a protective sheath or cover. The fact that so may inches of wire are visible or you think it is sufficiently protected is irrelevant. If there is a short on a battery cable, even the largest cable will turn white hot in seconds and will take a long time to burn through. A lot of heat can be generated in that short time, easily enough to cause a fire. The fact that you may be using heavy gauge cable is even more reason to be fuse or C/B protected because it will take longer to burn through. You might want to do a little reading on reserve capacity. it states how long a battery will put out power at a given amperage and it's usually very high amperage for a pretty long period of time. Anyone who thinks it's OK to not use fuse protection is either very uninformed or very lucky.

BTW, the small fuse mentioned on the back of your stereo does protect the device from a large electrical jolt, but it does nothing to protect the wire between the battery and the radio and that is still subject to a shorted condition and the loss of smoke.