The bag protects your board from bumps & bangs & chips etc. but as soon as you take it it out of the bag, for example, the narrow steps with high walls and tight bends at South Fistral. No matter how careful you are, you can guarantee it strikes the wall quite often especially with a longboard and what with meeting someone coming the other way it happens.
Also there are collisions in the water that happen now and again which sometimes cannot be avoided.
Uncovered rocks that you cannot see under the water, South Fistral has a few at the moment where the sand has washed away.
Some places there is no grass and when you take it out of the bag you have to put it down on concrete or tarmac which causes scratching.
Your board can also receive dents when you fall off.
The bag does protect the paintwork on your car from a salty board after a surf though.