The Art of War is useful in any area in which competition takes place. Since competition takes place in every area in which people are compared to one another, this includes every aspect of life.
I personally have written books apply Sun Tzu’s work line-by-line from areas as diverse as sports, romance, and parenting teens. I have also done a version for teens on managing the problems of growing up.
Sun Tzu’s big idea is that all competition is a form of comparison and the human brain works in a certain way when making comparisons and choosing a course of action. The first part of the book discusses the general way in which meaningful comparisons are best made. In the latter parts of the book, a lot of its lessons are very situation specific, but the situations are so common that they can be found in any competitive arena.
There is no decision that we can make without making comparisons. The question is: what needs to be compared? In making decisions about people and groups of people, working together or against one another, Sun Tzu breaks what is going down in a very logical way that is consistent with the latest thinking in human psychology.