You do understand that the cushioning in sneakers wear out much, much sooner before the soles wear out, right? That's why frequent runners will get new running shoes every few months even though the soles still look almost brand new, because once the cushioning in them are gone, the shoes are worthless to them as they'll cause them injury. Same with tennis shoes. Cushioning is very important to tennis shoes as they prevent knee, foot, and back injuries. And just like running shoes, the cushioning in tennis shoes will wear out far before the soles will. You won't be able to visually see the wear in the cushioning as you can in the soles but you will certainly FEEL it and your feet, knees and back will likely start hurting.