Most people initially seek psychotherapy when they are experiencing some kind of acute distress, with the hope that the psychotherapy will "fix" them or some how make them better. Although there is abundant evidence that psychotherapy is very effective for assisting people to reduce their distress, it is also a valuable way to enhance the quality of life beyond "normal".
I believe that there is a continuum of mental health ranging from people who are extremely unhealthy to people who are extremely healthy, with most people being somewhere in the middle, or "normal". I believe that no matter where we are on this continuum of mental health, we always have the potential to become more healthy. The pursuit of becoming more healthy, (even if we do not manifest any obvious mental health problems) is often called personal growth work or spiritual growth work.
As we become healthier, along with experiencing decreased distress in our lives, we come to experience greater fulfullment and deeper satisfaction. It is accurate to say that healthier people experience more happiness than less healthy people, but it would be misleading not to note that healthy people also experience deeper pain and sadness. However, the pain and sadness, along with the happiness, joy, and a full range of other feelings contribute to a richness of experience that is best described as fullfilling.
Along with personal growth towards increasing health comes an increase in spiritual experience. These are not spiritual or religious beliefs, but rather spiritual experience and awareness. They are compatible with virtually any religion and indeed the experiences are often described in various religious or wisdom traditions.
When I work with people in psychotherapy, personal growth is always an aspect of our work together. In my view, it really cannot be separated from what we are trying to achieve. Some of my clients come to see me in a state of acute distress but come to realize the value of pursuing further growth once their presenting problems have resolved. Others come to see me with little acute distress in their lives but rather a desire to accelerate their personal growth. (Others are quite pleased just to have relief from the difficulties that they came to see me about, and for practical or other reasons end their work with me at that point, with my full support.)
Personal growth work is most often pursued by adults in individual psychotherapy, but can equally be pursued through couples or family therapy, or for children through play therapy. Couples have a particular benefit of being able to facilitate the growth with each other between sessions in a way that is more difficult for individuals to achieve.