To protect the wood and prevent fires, he sets the thermostat at the lowest level that does the job. You just mold it and press it in place. You can fix almost anything with it. Even the most assiduous scraping and sanding can't vanquish mold and mildew that have nestled in wood fibers. His final prep step is a gentle rinse with the hose to wash off paint dust, bleach and dead mold.
Some people use a power washer, but it's just too strong.
You can write your name in a clapboard with a power washer. They're great for masonry, but I would never use one on wood. The water repellent, often a wax, keeps the wood from shrinking or swelling as much when it rains, so the paint stretches less, stays intact and grips the wood longer. The preservative kills mildew, which could grow into the top paint layer and ruin its look, and fungi that cause wood to rot. There is a wide variation in formulas on the market, however.