Google "How to polish Lee Collet die" then at the top of the page click on "images". This will take you to a internet world of polished Lee collet dies. (and a wealth of information)
https://www.google.com/search?q=how+to+polish+lee+collet+dies&source=lnms&tbm=isch&sa=X&ei=PpZvU-yRHKm_sQSUtIHoBQ&ved=0CAkQ_AUoBA&biw=1024&bih=643#imgdii=_
Below the collet and mandrel have been polished with the results in photos.
"What are the best dies for reloading .223 rem"
http://www.shootersforum.com/handloading-equipment/56252-what-best-dies-reloading-223-rem.html
When it comes to getting information Google is your best friend and all you have to do is ask.
Meaning you asked your question here in "one" forum, and by Googling the question you get all the answers from the entire internet. By going to images it lets you look at the most promising information.
Now find the photos of the cases with marks on the neck, deburring and polishing the inside and outside of the collet helps eliminate some of these marks and makes for smoother operation.
Just remember Google is always you best friend for information.