I was cutting my 3T Dorico Ltd seat-post to a required length earlier. Its not really my personal preference to an over-length and uncut seat-post sitting inside the seat tube. One of the main reason is that it may caused funny noises when the frame is under heavy load during the ride. Others maybe say you can save a few grams there.
Once it is cut, you will notice the wall thickness had been greatly increased for a greater strength. The thickest part of the post is at its rear end. Its measured at 5mm. It is a general design concept that the front and rear end of the post to be thicken to maximize its strength.