It won't hurt if you install a fuse on the negative lead, and the wiring harness that ships with most Amateur mobiles has two fuses.
The fuse on the negative (ground) lead is only really required on installations that connect directly to the vehicle battery.
The reason for the fuse, is that if the vehicle grounding from the battery to the car frame/engine should fail, either partially or completely, the radios negative lead "ground", in some cases, become the return path to the battery for the vehicle, causing the wire to burn.
This is not an issue for radios connected to power supplied, the vehicle chassis, or batteries not in a vehicle.
ALWAYS FUSE THE POSITIVE LEAD!
Batteries that have not been charged don't last long!
Take care of your batteries. Keep them clean and properly charged.