Need? Probably not. Want? Yes. Not sure about this one, but most auto-detect or just directly handle the voltage without telling the device. And then you can reasonably not care or worry less about what outlet you’re plugging into.
I have a friend that has a bad habit of plugging into the wrong/incorrectly wired/labeled/code breaking outlet and frying his stuff. Usually was with PC power supplies though back in the day. I gave him a voltage detector for his birthday once as a joke.
Has not yet happened to me because I don’t just stick into any available outlet (cough), but at the same time, after seeing and hearing stories like from my friend there, any cell phone charger, battery charger, or the like I look for 120-240v compatibility if I can get it.
Plus, would sort of suck if you had a 120v charger, got into a place, and wanted to charge up, and they for some reason only had 208v or 240v.
I’ve heard some people say they look at the voltage and frequency range as a sign of quality too, though not sure if there’s any truth to that.