Unlike most people, I don't drink coffee. Just don't like the taste. Never did and never will.
Tea, on the other hand, is a different story. While I sometimes drink hot tea on a cold night, my drink of choice most of the time is iced tea. I make my own from all sorts of different kinds of teas: flavored and unflavored, green and black and white and herbal, you name it.
Now I never add any sugar to my iced tea--the somewhat bitter taste is what I like about it. And I don't add milk or cream to hot tea either.
Different teas provide different benefits, but it's been well known that tea is loaded with antioxidants and other compounds that may increase the energy and calories you burn; regulate your blood pressure; help to prevent cancer, heart disease and clogged arteries; lower cholesterol; and reduce your risk of stroke, lung problems and Alzheimer's and Parkinson's Diseases. The list goes on and on.
There are some recent studies (click here for an NPR article on one of them) that show that milk proteins may bind with the flavonoids in tea and make it harder for your body to absorb the good stuff and give you the benefits that you're looking for from tea.
There are some experts, as is the case with most studies, who dispute these findings. They say that the amount of milk that most people put in tea is minimal, so it probably isn't an issue.
Still, you may want to enjoy your tea milk-less just to be sure you get the full effect of the benefits of tea. As for me, I'm just going to keep doing what I've been doing.