I wrote about my struggle with mental health issues because it is absolutely the reason I am going into social work. I wrote about how it has motivated me to help others experiencing the same struggle, as a strength that will help me understand their experience. I also wrote about how AA is an important part of my self-care and support system.
I don't know if that would be recommended in all cases. I was applying to Jane Addams, which is a school that believes really strongly in social justice and diversity, so I knew going into it that my story might make me a strong candidate. And I did get in. Ultimately, my experiences with mental illness are such an integral part of my story and the reason I am going into this field. I couldn't imagine not writing about it in my Personal Statement.