It's kind of what it says on the tin! The seller is the owner of the road but they are giving the buyer a right to access their plot over the road. No real disadvantage to this, the road will be a shared road, might be no harm to make sure that if the buyer needs pipes or services to their plot that this is also covered and an agreement put in place for future maintenance/insurance if needed. The seller would also be able to give a right of access to other people.