Local Transport Bill [HL]

Why the distinction between Clause 68, which is about any two or more authorities, and Clauses 70 and 71, which could be just one authority? I understand the argument about flexibility, but there is a contrast between the two clauses. I do not understand—perhaps my noble friend could give an example—the kind of situation where it might be appropriate or necessary for it to be only one authority under Clauses 70 and 71, as opposed to two or more.