Social psychology is a wonderful, enchanting field.
It is full of delightful experiments which often reveal deeply illuminating facets of human nature.
The experiments are usually so well done that it is hard to argue with the results.
Many people in mental health fields, such as psychiatry, have not studied social psychology. I never took a course in it myself. I feel like signing up for one now.
Applications of social psychology research could apply to treating anxiety & depression; resolving conflict; improving morale; reducing violence on a personal or social level; improving family & parental relationships; building social relationships, etc.
My only slight criticism of typical social psychology research is that it tends to be quite cross-sectional, and the effects or conditions studied are most often short-term (i.e. results that could typically be obtained in a study lasting a single afternoon). My strongest interest is in applied psychology, and I believe that immediate psychological effects can be important, but long-term psychological effects are of greatest importance. The brain works this way, on many levels: the brain can habituate to immediate stimuli, if those same stimuli are repeated over weeks or months. Learning in the brain can start immediately, but deeply ingrained learning (akin to language or music learning) takes months or years. So some results from a day-long study may only be as deeply insightful as administering a medication for a single day -- the effects haven't had a chance to accumulate or be subject to habituation.
In any case, I strongly encourage those interested in mental health to read through a current social psychology textbook (examples of these tend to be very well-written, readable, and entertaining), and to consider following the latest social psychology research. The biggest journal in social psychology is the Journal of Personality and Social Psychology.