Yeah, it's one of those small steps that makes a huge difference. People like @patricia_chen67 get lucky with their tap water, but most of us don't have that soft water. It's like anything else, skimping on the last step can wreck all the careful work you did before. I see it with people who cheap out on the final rinse for their car or use a bad towel to dry good glasses, leaves streaks every time.
Oh man, that is such good advice. Tap water leaves spots and mineral marks that can ruin a perfect shot. I learned that the hard way after a whole roll came out with weird dried water stains. Your uncle knows what's up, it's a tiny cost for a huge difference in quality.