How can you guys use a Naniwa SuperStone OTB with residual sticker glue on the surface?

I know first hand that these stones will act better when lapped a few times too. The Naniwa Choseras are the same way, in fact the Naniwa Chosera barely work at all until lapped.

Flatness is only one reason to lap a stone.

Another thing worth noting is that the edges of stones should be rounded after flattening has been done. If you don't do this your razor will be elevated by the high corners and not be allowed to make full contact across the bevel. In the knife sharpening world we call this "sharpening on rails".