"all energy finally ends up as heat"
With power, this golden rule is no exception. What is desired is to reduce the amount of heat generated through losses on the network.
The losses could be caused through a network not designed for or capable of supplying the demand placed on it, or simply a demand with properties that cause 'above normal' losses.
With the first avenue we should explore cabling that may be old or specified for an industry that was not very machine intensive, whereas the second avenue is a building now used as a computer centre with a far-from-ideal load.
With both examples the result is heat being dissipated which in turn is loss. Furthermore, heat can also shorten the life of electrical installations, sometimes dramatically.
When it's a loose connection, being a high resistance and therefore a large voltage drop resulting in a large amount of power being dissipated, it comes as no surprise when a contact is melted to insignificance. But when all connections are tight, currents are well within the installation specs, and heat cameras show no hotspots, but items within an installation are still being "blown to heck", then serious questions start surfacing.
The final level of heat damage is simply that electrical installations cannot cope with the load and start burning, and if the installation does not contain this then the loss is rather catastrophic!
It's understanding the causes of how the heat is generated, and how to reduce it, that probably best describes power quality engineering. Having said this, it is extremely important to know where the energy is being wasted before being able to put an end to the waste. Sometimes the heat is spread over such a large area the waste appears negligable, but our next section shows a flaw in this thinking!