I think the more critical you are to the business, and the more pressure and responsibilities you have, the more critical it is to worry about work/life balance. People aren't robots, and we don't have infinite capacity to work, our ability to make rational decisions, understand the market, customers, employees, think critically, etc. is all dependent on having a healthy working brain- and that requires rest and recreation.
For founders, and really anyone heavily invested in early stage startups or companies looking for a lot of growth, responsibilities are 24/7 and the line between work and life get blurry, and it's a lot more difficult to make sure the balance is there, but also a lot more important.