Most renewal language will require the franchisee to execute the "then current" form of the document. So, if you have material changes to the franchise agreement that you want incorporated into all agreements, an early renewal can be a good way to bring your existing zees up to the current franchise agreement requirements. 

Of course, you could also just simply amend the agreement.  But this is problematic in two ways: first, you must generate and keep track of individual amendments to the franchise agreements.  This can create administrative challenges.  Second, franchisees usually like the game of give and take.  If the amendment is strengthening certain franchisor rights and the franchisee is not really "getting anything" in return, you could face some push back.

In the case of an early renewal, the term of the franchise agreement will "reset" to the extension term, thus giving the franchisee a "new" term in return for executing the then-current agreement.