Electrical System Harmonics
A particular reason why the electricity companies think harmonics are bad is that they have to supply them (which means a generally slightly thicker cable on average) AND they can't usually bill the user for them. There are exceptions of course (for higher energy users) and they are encouraged (by the cost of their bill) to keep harmonics low and power factor as close to unity as possible.

A harmonic is a term that nearly always applies to a non-linear load distorting the normally sineusoidal load current. Basically it's not a higher power consumption but it does mean the infrastructure has to be able to cope with the basic billable currents and the generally non-billable harmonics: -