Many 9-5ers minds are always thinking of how to escape anyways, so at least you have something tangible to think about if you already have that business
Don't get me wrong, I enjoy thinking about how to improve my product, new marketing ideas etc., the issue is more how it affects the rest of your life, where your attention on other aspects of life might be diluted, as a result maybe you will spend less time thinking, for example, about what nice thing you could do for your partner.