Standby consumption was a genuine problem in the era of cathode-ray televisions and early set-top boxes, some of which drew nearly as much asleep as awake. Regulation and better power supplies changed that, and much of the advice has not caught up.
What barely matters now
Modern televisions, laptop chargers left plugged in without a laptop, and most small appliances draw very little on standby — typically under a watt. Unplugging them is not wrong, but the saving is close to invisible on a bill.
Phone chargers in particular have become a folk villain out of all proportion to their consumption.
What still does
The meaningful loads are the things that are not really on standby at all — they are running quietly. Set-top boxes that keep recording, games consoles left in rest mode with downloads enabled, older desktop computers asleep rather than shut down, and anything with a compressor or a heater in it.
A second fridge or chest freezer in a garage is frequently the largest single overlooked load in a house, because it runs constantly and is often old, poorly sited and working harder than it should.
Electric towel rails and underfloor heating left on a permanent schedule belong in the same category. They are not standby; they are on.
How to find yours
A plug-in energy monitor costs very little and settles the question in an afternoon. Measure the things you suspect rather than switching off everything indiscriminately.
The useful outcome is usually one or two discoveries, not a long list — which is a more sustainable change than a nightly ritual of unplugging things that were never costing anything.