The fuse protects the wire from overcurrent conditions that would cause it to get hot and potentially cause damage or a fire, such as a short. If the wire in the harness for your lights is sized for a 15amp fuse and you connect it to a 40 amp fused circuit you have undermined the protection.
I...
Before they added the rocks it had huge mud holes all along there and it sucked for the first 2 months after the snow melted. Way nicer to deal with some small rocks than that mess.