The difference is that if you sold your company for $x million you can just put your money in a lowish risk investment and do literally whatever you want for the rest of your life with very little stress provided you don't go crazy with the yachts and strippers.

If you have recurring revenue of $x thousand per month from a product or service where revenue doesn't scale with hours worked you still have stress because if your customers leave (for example a competitor launches something better or cheaper) your revenue drops. So you still must spend at least some of your time working on that.