When driving a single LED from a battery, efficiency is key.  Efficiently making use of the battery’s energy and efficiently converting it to light output prolongs battery life, which reduces cost and hassle for the end user.  While high efficiency switching power conversion is the first step in this process, dimming is a second step just as important as the first.  Dimming allows the user to reduce the light output, and thus the battery power consumed, when they don’t need such a bright light.  This combination of dimming and high efficiency power conversion gives such items as smartphones and glucose meters a sufficiently long battery life.