Questioning why you do things is important for several reasons.
EJCC had some good points, and they are especially interesting coming from an ESTJ. As you read about ESTJs, many people (unfairly) characterize them as out of touch with their emotions, not introspective, or overbearing. She is a great example of someone who has looked at some of those issues and used them as as an opportunity to educate others and also to balance out those tendancies where she finds them.
We don't have enough lifetimes for the amount of mistakes we could make. If we can watch and understand our own positive and negative tendancies, as well as what is working/not working for others, we can save ourselves a lot of pain and a lot of irretrievable regrets and unfixable errors.
Some feel it is their own business and if they make a mistake, it's their own problem. The flaw in that reasoning is that every decision we make has an impact on other people in some way. Who we marry isn't just our own business: we forever alter our immediate and extended family dynamics, we bring children into the world who are affected by what kind of parents ourself and the other person makes individually and in combination, we affect the education system, the medical sytem, the justice system and the climate of the country by what kind of kids we produce, we affect what kind of work gets done in the world by us as a couple, and we affect those in our circle whose lives we could improve/deteriorate by teaming up with another person. That is just one small example.
The bigger a decision, the more it will affect others than only us, which is why it is up to us to properly research, analyze our own tendancies, consult others who have experience or regrets or wisdom etc.
We also become much more comfortable with ourselves as we grow able to predict why we act and feel as we do. When we are more personally comfortable, we are then able to focus on the needs and interests of the people around us. Our own discomfort is really a form of self-centredness, even though we rarely would think of it in those terms. Therefore, when we become more confident and secure, we also become more selfless. At the same time, we also are better able to take care of ourselves properly (emotional needs, carving out appropriate time for self, treating our bodies well etc). This too is going to have a better effect on the larger society.
Our insights to why we act as we do also give us clues for understanding why other people act in the way they do and give us more empathy and kindness than we could otherwise feel for them. As we become aware of how others have overlooked our shortcomings or contributed to the good things that we have, it helps us to extend grace towards others when they need it and to think of how we can provide for their needs too.
No man is an island. Each of us individually contributes to the well-being or the downward slide of our culture or society. However, even if it were for selfish reasons, figuring ourselves out usually contributes to better relationships, a greater acceptance of who you are while shoring up your negative traits, more teachability, better character, a more rewarding work life, and often more money.