If someone is stalking or harassing you, they might be able to use information in your bio to further their abuse of you.
I don't get why people are arguing about the point of this feature.
You don't want it. Don't use it and use your existing bio as it is.
People that want to use it, we get more granular privacy customizability on Telegram. That's all
"Bio" technically is a heads-up message about you for people who doesn't know you. It's not an "about" or "current status" or "what's in your mind" message that your friends wanna keep checking. Write only public stuff. If you think you're writing something that needs a privacy settings, just don't write it.