Technically, the smoke is in the components. When they fail, it may cause the wiring to smoke as well.
At the age of 63, I've only been making a living out of radio engineering since 1964, and I built my first radio 57 years ago......I chair a European Standards committee on radio equipment, published some 37 different papers and articles, generated 23 patent applications, have consulted for UK DTI as it then was, referee papers for the IET (used to be the IEE), and represent another organisation at the International Telecommunications Union, so I claim some knowledge.....
I still say it's better to keep the damn thing off.