I know that modern electronics (smartphones, laptops) have dual voltage and frequencies (100-240V 50/60Hz) however when you discuss appliances (toasters, blenders, refrigerators, clothes iron, dishwashers, dryers, etc). those are region locked (besides plug type) into a single voltage and frequency. For example: if you have a electric blanket that only supports 120V 60Hz, you can't plug that directly in a 230V 50Hz outlet as that'll blow the fuse.

There are ways to circumvent that restriction but involves using transformers to lower the voltage (step down from 230V to 120V), as stuff like hair dryers or microwave ovens can be damaged upon using the wrong grid. If moving abroad permanently, it's best to purchase new appliances that supports their electrical grid rather than importing them if you have only 120V versions whilst living in a country where 230V is standard.