Disagree completely.
You,
@steingar, have a plane that you know very well, have done hundreds of takeoffs and landings, and have an "sense" of what your plane can do that by now seems intuitive, and if you find yourself having doubts, it's because that corner of your brain where that knowledge lives is speaking up and saying "No". I know that feeling too, after flying the same plane for a long time. I have that "anything >2000ft is doable even at max gross on a hot day" intuition. But not everyone has that luxury, maybe you fly whatever plane the school has available and they're all different. We train students to do these calculations because there are plenty of times when you *do* need to ask the question and the answer is not blatantly obvious. Same goes for things like fuel calculations, W&B, you name it.
I'm plenty familiar with our 172's performance at sea level in Alaska. But when I was planning my departure from Truckee in the summer, yeah, I actually dug out the book and ran some numbers. Turns out I would need about 1500 feet on a runway that's 7000, which is laughably easy. But it was a regime I'd never taken that particular plane into before, so I wanted to ask. Plus, it was fun to actually watch the runway markers on takeoff and see the calculation come to life for real.