The only people who graduated from my course with a 2:1 were those who did placement years. Nobody got a 1st, and the rest got 2:2 or below. The big thing it gave me was the ability to see through all the crap they set us to do in our final year, and focus on exactly what I needed to do to get the best grade possible. It also teaches you that in engineering, academia is very far from the the real world of work.
I would also echo the comments about knowing your place – nobody likes a know it all undergrad/grad.