Buddhist concept of mindfulness

There is a concept in Buddhism known as mindfulness (satipatthana). In it's simplest form it means to be in the moment at all times. A person should always "live in the moment" so to speak. Is this something that should be practiced? How is it beneficial and/or dangerous?

To be mindful, one has to have triggers to keep the mind in the moment. How many times have we just zoned out watching inane stuff on the television or while driving? Being mindful this does not happen. We have a predetermined trigger that reminds us of being in the moment, whether it is counting our breaths, an alarm, or something else, something that reminds us to be mindful. To be mindful we must see all around us, absorb and filter it, and gather wisdom instantly. This short-circuits reflecting upon past events. Not essentially a bad thing, but definitely an adjustment. The practice of being mindful requires constant vigilance. And that, to me, appears to go against what is the essence of Buddhism. How can one be mindful and be true to Buddhist principles?

Picture the scenario of living one's life in a potentially dangerous city. One is aware and aloof at once. Danger is all around, and the mind is prepared for it and scanning for it, but at the same time one is not concerned by it. One sees all and filters it into categories of normal, new, dangerous, and boring. The mind registers the prominent stuff. One is mindful.