When we are putting tile in a tub surround we focus on problem areas that we have seen traditionally have problems with water penetration and moisture resistance. Where your tub meets the backer board and along the edge on the outside corners of the tub are problem areas. In your minds eye imagine using this tub, imagine a child playing in the tub, the splash, the waves...there will be a lot of water action in those spots. We mitigate these issues by installing waterproof Kerdi band and also using a water proof sealant to manage the moisture in these areas. This is a full Schluter Systems product, we're not just throwing up cement board or sheet rock and calling it good. Don't skip out on the water proofing even though "it's just a tub surround." Tile is forever, so think like a rain drop!