Lee molds of the tumble lube design are supposed to require no sizing if you're casting with the alloy Lee specifies that is on the data sheet that comes with your mold, and they may not need sizing with the alloy you're casting with it just depends on your size requirements that best fit your firearm and what the mold is dropping.
However, I've never found that to be the case with the alloy I cast with before or after I started powder coating my bullets, so I just size all my bullets for constancy. I have around 25 Lee molds in two and six cavity as well as molds for pretty much ever other commercial maker, and the Lee molds cast bullets of good quality and shoot as accurately as some of my more expensive molds.
