Precommiting is useful in many situations, one being where you want to make sure you do something in the future when you know something might change your mind. In Cialdini's "Influence," for instance, he discusses how saying in public "I am not going to smoke another cigarette" is helpful in quitting smoking.

If you think you might change your mind, then surely you would want to have the freedom to do so?

The whole point is that I want to remove that freedom. I don't want the option of changing my mind.

Another classic example is the general who burned his ships upon landing so there would be no option to retreat, to make his soldiers fight harder.