All of us have various parts of ourselves that serve a purpose in our lives. Sometimes they work together cooperatively, and sometimes they are at odds with each other. (And I'm not referring to Multiple Personality Disorder, now known as Dissociative Identity Disorder, here). Think of a "part" as a state of being. One part of your personality may want to do something, while another part of you wants the opposite. For example, one part of you may desire to diet and lose weight, while another part of you isn't yet ready to change the chocolate habit.
The value in learning how to do Parts work is that: (1.) You can re-do paintul memories by activating the "Wise, Strong, Compassionate Part" of yourself to "go back in time" via visualization, providing something you may not have received in the actual experience, such as acceptance, love, nurture, comfort, encouragement, truth, or safety; (2.) You can more easily set healthy limits for any part of you that turns to food, alcohol, shopping, TV, or any other mind-numbing substance or activity; (3.) You can have greater control over your emotional reactions so you are less likely to do things that push others away or to invite someone into your life who may harm you. (4.) You can also learn to listen to your truest self and make healthier decisions regarding how to live your life and who to have in your life.
This is a paradigm shift for many people, and finding this Wise, Strong, Compassionate part of yourself will create new neural pathways in your brain associated with feeling valued and at peace. The more you practice it, the stronger those neural pathways become. Many people I've worked with have told me doing "Parts" work made a profound difference in their lives.