For me it depends on the smell and the inside diameter of the bowl. Some blends I just can't do, so the first thing I do is ream it with my pipe tool. If your o.k. with the smell of the bowl leave it alone. If I can't get my little finger down the bowl, it's time for me to ream it.
Ive only gotten one estate pipe, and the cake was over 1/4th inch thick and very uneven. I had my friendly pipe store guy ream it out and he threw in a sample of Orlik Golden Sliced, which I enjoyed immensely. I smoked out of said estate pipe for the first time today and it is much larger than I am used to, but very nice.
My only issue with heavy cake / 'dirty' pipes is not knowing their history and what has been inside the bowl as they have sat for an unknown period of time.