AMPk is a cellular energy sensor, activated mostly at low energy states. Its activation often depends on ratios such as AMP/ATP and NAD+/NADH. The main purpose of AMPk activation is to restore cellular energy.
“Thus, any change in cellular energy status activates AMPK, leading to concomitant inhibition of energy-consuming processes and stimulation of ATP-generating pathways to restore energy balance” 
Stressors that can reduce cellular energy include nutrient deprivation (i.e. caloric restriction), hypoxia (low oxygen conditions), exercise, ischemia, cold exposure, heat shock, fasting, metformin  and several others.
High levels of AMP/ATP (low energy status) lead to the activation of AMPk, which triggers processes such as:
– increased oxidation of fatty acids,
– increased glucose uptake inside the muscles,
– increased mitochondrial biogenesis ,
– reduced cholesterol synthesis,
In my current view, higher activity of AMPk is a good thing. However, I assume that most people lack the exposure to such stressors – that I mentioned above. Chances are, then, that AMPk activity inside their cells is reduced or inexistent. Here, I want to briefly discuss the findings of a study relevant to the topic.