Tremendously different if you've ever pitched. That cool down period in between innings. That's the difference.
Have you ever noticed that during a rain delay, quite often the previous pitcher is removed for a new one? This is why. It's hell on a pitcher's arm to warm up, throw full tilt, cool off completely, then go right back at it. It's also why it's an extremely bad idea to warm up a relief pitcher unless you intend to use them. Those warm-up throws also count as bullets in the gun too.