Are cases that cover the front of your iPhone bad?

I have an iphone 4.
I was told that phone cases that cover the front (top and bottom) of your phone are bad because it cuts of some of the connection or service of it or something… Is that true?

It can be bad because your phone can over heat due to being all the way covered. So new air doesn't flow through so it gets really hot. Other than that I haven't heard anything thing else about full cases being bad.

No that's not true. Although I do highly suggest a case that covered the front simply for protection of the screen.