I usually split mine into 1.5-2.0 ounce chunks so that I can spread them evenly in the smoke box, but I am not sure that is necessary or not. It is just something I have always done.
I think for a long smoke like a Boston Butt or Brisket, leaving the chunk whole would be good. But for shorter smokes like ribs, poultry, etc., I think splitting the wood would be a good idea.