One of the themes I have harped about on this blog has been the issue of opportunity costs. When a great power gets itself over-committed in a lot of costly and time-consuming commitments (and when it mismanages its economy in various ways), then it won't have the surplus it needs when an unexpected challenge (or an unforeseen opportunity) arises.
Case in point: the current floods that have ravaged Pakistan in recent weeks. The situation is by all accounts horrific, and could have significant long-term consequences for millions of people. It is precisely the sort of event that calls for a vigorous and generous U.S. response.
As everyone knows, the United States is widely despised among broad swathes of Pakistani society. Some of this hostility is unmerited, but some of it is a direct result of misguided U.S. policies going back many decades. As the U.S. experience with Indonesia following the 2004 Asian tsunami demonstrated, however, a prompt and generous relief effort could have a marked positive effects on Pakistani attitudes. Such a shift could undermine support for extremist groups and make it easier for the Pakistani government to crack down on them later on. It is also the right thing to do, and the U.S. military is actually pretty good at organizing such efforts.
The United States has so far pledged some $76 million dollars in relief aid, and has sent 19 helicopters to help ferry relief supplies. That's all well and good, but notice that the U.S. government sent nearly $1 billion in aid in response to the tsunami, and we are currently spending roughly $100 billion annually trying to defeat the Taliban. More to the point, bear in mind that the United States currently has some over 200 helicopters deployed in Afghanistan (and most reports suggest that we could actually use a lot more).
So imagine what we might be able to do to help stranded Pakistanis if we weren't bogged down in a costly and seemingly open-ended counterinsurgency war, and didn't have all those military assets (and money) already tied up there? It's entirely possible that we could do more to help suffering individuals, and more to advance our own interests in the region, if some of these military assets weren't already committed.
Of course, Obama didn't know that there would be catastrophic flooding in Pakistan when he decided to escalate and prolong the Afghan campaign. But that's just the point: when national leaders make or escalate a particular strategic commitment, they are not just determining what the country is going to do, they are also determining other things that that they won't be able to do (or at least won't be able to do as well).
Thus, another good argument for a more restrained grand strategy is that it might free up the resources that would allow us do some real good in the world, whenever unfortunate surprises occur. As they always will.