For AC motors, the lower voltage might mean they do not have enough power to turn, so all the power they consume becomes heat in the motor windings (and since they're not turning, there's less cooling).
For electronic power supplies, they might either pull more current to maintain the same output (again leading to more heating), might output a lower voltage (and DC-DC converters which consume that voltage might in turn draw more current, again leading to more heating), or they might even misbehave and output an oscillating voltage; they might also detect the power dip and shut down, only to power up again moments later, repeatedly.
A device in an idle stand-by mode is probably the best case, since it's using little power from a supply sized for a much bigger load.
I disagree with the sibling comment that the only protection from voltage dips is a UPS or similar; a simpler protection is an undervoltage relay with a timer, to convert the voltage dip into a power outage (and also prevent the power from being restored too quickly).
* The only protection available as a consumer add-on.
Sure, if the manufacturer wants to increase the cost on the BOM for their PSUs, they can use additional components to survive dips, but who does that on disposable electronic equipment? Hell, even "expensive" TVs don't. I quote expensive since you can now get 65" 4K TVs cheaper than a mobile phone, but that's a tangent. So if you are wanting to protect your electronic equipment with another device readily available that is just plug an play ease of use with no knowledge of electronics, what do you suggest?
I have a friend who did that; he put one of these relays on the apartment's power panel, so the whole apartment was protected against voltage dips or too short outages. It might not be a common consumer item, but it's a readily available device, AFAIK commonly used to protect industrial motors.
For AC motors, the lower voltage might mean they do not have enough power to turn, so all the power they consume becomes heat in the motor windings (and since they're not turning, there's less cooling).
For electronic power supplies, they might either pull more current to maintain the same output (again leading to more heating), might output a lower voltage (and DC-DC converters which consume that voltage might in turn draw more current, again leading to more heating), or they might even misbehave and output an oscillating voltage; they might also detect the power dip and shut down, only to power up again moments later, repeatedly.
A device in an idle stand-by mode is probably the best case, since it's using little power from a supply sized for a much bigger load.
I disagree with the sibling comment that the only protection from voltage dips is a UPS or similar; a simpler protection is an undervoltage relay with a timer, to convert the voltage dip into a power outage (and also prevent the power from being restored too quickly).