I stopped doing it like a month after I got mine and the food comes out exactly the same, maybe even better because I'm not adding extra time for no reason. The manual acts like you're committing a crime if you skip it but honestly who has three extra minutes to waste when you just want some frozen fries. My sister still preheats hers every single time and then wonders why her nuggets are dry, like maybe it's because you cooked them twice? I get that some models might need it for certain recipes but for 90 percent of what normal people make in these things it's totally pointless. The whole point of an air fryer is that it's fast, so why would I sit there waiting for it to heat up like it's a regular oven. Just throw the food in cold and add a couple minutes if you have to, problem solved.