Name tags are a necessary evil when visiting a conference. The security guard can see you paid, and people can read your name, company, and role casually. It is also a great way to store the day program and your lunch coupons.
But when on stage, it looks a bit weird. When presenting right that moment, when someone watches the online video of the talk 6 months later, when the entire panel consists of 12 people with the 12 white dots on their shirts.
Oh, and also ask people to take of their tags when posing for a group photo.
Art: Albrecht Drurer, Portrait of a young Venetian woman, 1505