it's best to have nice bearings in the bar, that way the bar will spin and the weights won't. Nobody wants to have any of their force production going towards rotating the weights (which can have a large moment of inertia) when lifting the bar. If you have a bar with good bearings, a minimal amount of force is required to rotate the bar while lifting it, thus allowing more energy to be directed towards the actual lift.
Granted a lot of people might think I just blew smoke up their ass... but I'm serious. Try doing a max clean with a nice olympic bar, and then again with a solid/fixed bar (where the weights rotate at the same angular velocity as the bar) and see which you can clean the most with, it will be the bar with the best bearings (if you really get into it, then bar whippiness can also have an effect).
Take home message, good bearings = less inertia to overcome during the lift = more weight lifted