My perspective on supervision
For me supervision is an explorative or collaborative review, with two people who are professional peers working openly together to explore, understand and appreciate the nature of the counselling relationship. I work with an open, Integrative Model of Supervision.
The practice of supervision means that details provided by clients are shared with another professional within the same field other than the counsellor concerned. However, overall client confidentiality is still safeguarded because any information shared in supervision is itself protected under a contract of confidentiality (and the personal, identifying details of the clients under discussion are not disclosed to the supervisor).
It is needed primarily to protect the counselling client, and also the counsellor as a professional working to provide safety and value to their client.
My personal experience of supervision so far in my career has been the enhancement of my skills whilst always giving me support and confidence within my work with counselling clients so I work within the BACP guidelines to provide this for my supervisees.