Is it neccesary to use a coaster when you are drinking out of a wine glass?

We have a coffee table in the living room and we like to drink while watching TV. We use coasters for coffee, juice, and every other drink that is served in a regular glass, but when it comes to wine, in a wine glass, i think we dont need one, while my partner insist on placing a coaster. is it really neccesary?