[esperent]

It's only useless if you consider all art, games, and educational tools to be useless. Which is a very sad outlook.

Art: they look beautiful and can be displayed.

Game: breaking it, or watching it being broken, is a lot of fun.

Education: I would say that a huge number of people have been inspired to take up glassblowing after seeing one of these. But not only that, they also serve as a great tool to demonstrate that an object's physical properties are often unexpected based on appearance. I would say a decent amount of people have been inspired to study physics because of this too.