Everything you might plug in causes a voltage drop. The larger the draw and the smaller the wires or poorer the connection to the mains, the larger that drop will be. If you plug a single LED light (very small draw) into a circuit capable of carrying 50 amps, that drop will be undetectable with any voltmeter. But if you put an electric space heater (large draw) on a 15 amp circuit with corroded plug or slightly burnt receptacle, you will easily find a significant voltage drop.
Whether the drop is significant of a problem, however, is another matter.
