Yes, I think it tends to make your hair dryer, brittle, and frizzy. Just don't use them too often but if you have too, it's best to use with heat protection serum or oil treatment.
I think it's bad but I do it anyway. I guess it also depends on how much you take care/treat your hair as well. I have fairly thin hair but if I let it to air dry it becomes really frizzy but when I blow dry it, it stays straight and sleek. But I know that in the long run I'm damaging it!