Since 1989 I have worked with over 60 immigration attorneys to assist them to document psychological extreme hardship and extreme and unusual hardship that U.S. citizen, and in some cases, legal permanent resident spouses and children will experience if their spouses/parents are inadmissible or deported and the spouse/children have to follow them to the claimant's native country. As a clinical psychologist in the State of California I can also document 212(c) rehabilitation, the presence of post-traumatic stress disorder, anxiety, and depression for political asylum applicants, and symptoms of psychological trauma for victims of domestic violence.
I have an invited article published in a special issue on immigration of the Children's Legal Rights Journal on the "Psychological Evaluation of Children and Families in the Immigration Context", (1999), 19 (3), pp. 17-25. My career in immigration law began at the age of 18 when I was given a work-study job as a file clerk for the Immigration Office in Boston, MA during my summer between my senior year in high school and college. When they found out I spoke Spanish they made me an interpreter doing deportation hearings, investigations, and interview for removal of conditional residency based on marriage. I did this for five years part-time. I was also an immigration attorney for 8 years, now inactive in good standing.
If you were to have surgery you would want a surgeon who has had much experience in performing the procedure that you need. To maximize your chances of winning your case you want a psychologist who has had experience working with the best attorneys and who knows the law and keeps current with country conditions that can impact your case.