Voice and tone help distinguish you from everyone else. Without them, you’ll start to sound generic, like those late night TV infomercials. Or worse, like your competitors.
Voice is your forever personality. It’s why your mother can recognize it’s you when you call.
Tone is the difference between how you sound when you call your mom on a good day and how you sound when you call your mom while PMSing. You’re still you, you just sound a little more pissed.