The original question had to be edited. I would suggest that the "no front wars" in both contexts have many points of similarity. Those in the position of power invoke the "no front war" in order to communicate the ongoing and persistent nature of the conflict. In Vietnam, the "no front war" was employed to communicate the unconventional nature of the conflict to a public that had only been exposed to conventional warfare. In the War on Terror, the frontless element is used to explain how "the enemy" can strike at any point and in any location. The "no front war" in this context is meant to enlist the engagement of the public in support of the pursuit of the dispersed enemy.
Those in the position of power benefit greatly from invoking the "no front war" approach. In both contexts, the lack of a defined front reflects how the war will remain ongoing. In the context of the Vietnam War, being able to communicate that the conflict lacked a defined front was intended to convey the unconventional nature of the war. At the same time, it was also used to buy time with the American public in order for leaders to determine what the metric of victory would be in an ever changing context. Being able to suggest that there is no "front" gave leaders time to assess and define metrics for victory. Yet, such metrics could not be effectively communicated to the American people.
The War on Terror is able to invoke a "no front war" to show that terrorism and its threat exists everywhere. This widens the flexibility of governments that wage the conflict in trying to counteract an opponent that operates in a borderless setting. For example, threats in Afghanistan and Iraq have now broadened to places like Mali. There is no "front" that limits those in the position of power. Being able to use a "no front" approach in the War on Terror helps to increase the ability of the government to commit itself without having to face much in way of opposition. Both conflicts were able to increase the ability of those in the position of power to engage in the conflict without stagnation of effort.