Literally the next paragraph of my post addresses that. If you are accurate enough to predict your life spending needs to within 16% of the actual number, more power to you and go on living. It seems like a tall order to expect people to predict multiple decades into their own future though.

However, let's do the math: if you expect to live to be ~80 years old and are currently 40, then with the 200k buffer you mentioned you only have 5k per year or ~416/month. There are numerous eventualities that could eat up such an amount, like unforeseen illnesses or children or both. Having a bigger buffer means you will have a bigger chance that you will not need to stress out over unexpected costs.

So the point (IMO, YMMV) is not to maximize the number but to minimize the chances of life's surprises catching you off guard. The extra money buys peace of mind. (And yes, after some amount any extra money is just excess and time would be better spent enjoying hobbies/romantic partners/friends/children, but how much that extra buffer needs to be can only decided by everyone for themselves)