Protein is a building block of the body and is in many cells, not just muscle. Not getting enough protein is definitely not a good idea if you're trying to build muscle. Similarly, excess protein doesn't do anything for your body and is just processed by your liver before being excreted.
That said, carbohydrates are necessary to "power" your muscles while you're doing a workout. You can get the energy from fat or protein instead but it's best if your energy comes from carbohydrates. That said, some people (myself included) are not particularly good with carbohydrates when they're not exercising, so eating carbohydrates just makes them more tired and hungry. I've found that if I eat a lot of carbs in the morning, I feel lazy and just want to go back to sleep but if I don't eat much in the way of carbs, I have plenty of energy. I do eat carbs before, during and after my workouts though or I can't get through them without becoming exhausted.
(Website by Marc MacYoung, not me)