Well the idea is that you're paying for someone who is both qualified in dealing with mental health issues, and is completely unattached to your life to provide a confidential, non-judgmemtal outsider perspective on your life.

The people who know you almost certainly can't provide that level of support in your life, and many people need that space/perspective to help them recognise their issues, or push them towards the correct solution to resolving them.

It's not everybody's cup of tea, it ain't mine, but for those it does work for, it works well