A fuse on the negative lead is protection from a hard fault, but there can be conditions where a ground is just "iffy" and currents less than where a fuse would open flows through the radio chassis. So the radio sits there and "cooks", or experiences fluctuations of supply voltage which generally detracts from radio operation and reliability. Grounding near the battery ground point reduces effects of ground faults.
Mark K5LXP
Albuquerque, NM