Read the post Mr. X put up about the false notions of dieting. Always keep in mind that what works for your buddies won't necessarily work for you. Every jackass in my gym swears by a different diet and supplement routine. The only ones who stand out from the crowd are the guys who lift hard, eat clean and get adequate rest.
Having said that, sure, beef has it's place in a mass building diet. You can't beat red meat for gaining size and strength. Sweet potatoes are delicious, but white potatoes aren't the most wonderful choice. But if it's a matter of simply getting in enough calories, go for it.