Energy harvesting is a series of processes including collecting energy around us, converting it to electricity and operating small equipment with it. We all know that we can generate a lot of electric power if we use fuel, but that is not called energy harvesting. Energy harvesting does not include electric energy generated from conscious human effort either. The key idea here is being able to generate electricity "unconsciously."
Careless harvesting may end up overburdening an energy source by trying to get as much energy as possible. With all honesty, it is impossible to generate a large amount of energy through energy harvesting anyway. Such attempts would result in creating devices unrealistically large or costly, defeating the purpose.
Therefore, energy harvesting only makes sense when it is done through the effective and thrifty utilization of small amounts of harvested energy.