Did you read my post? When remodeling, you sometimes have to install, remove, and reinstall a toilet a few times. Scrapping off the wax, getting a new one, and resetting the toilet is messy. The waxless can be reused numerous times. It can also help if the flange not quite level or recessed as the thing fits down into the throat of the drain line. My flanges were fine, but because I was trying to keep things useable as remodeling, painting, tiling, fixing the subfloor, etc. I chose the waxless. If you pipe is old cast iron, it might not seal well, so probably wouldn't be the best choice...there a wax ring is still king (and cheaper). The inside of the pipe needs to be fairly smooth and clean. If you were using something like a Caroma with a 3" internal trap, it probably wouldn't be a good idea as there'd be a restriction, but it is as big in diameter (bigger actually) than that in most toilets so hasn't presented a problem, at least for me.