Confidentiality and breach of duty
Knowing information about a client and mistakenly revealing it to someone else is a constant risk.
Imagine, for instance, that you freelance in the PR sector, and are advising a couple of clients who operate in the same industry (they could be competitors). In spite of your best efforts, you disclose a new development or product from the first client, which could give the second client a competitive advantage.
Should the first client discover this, and believe that they have lost money as a consequence, you might be sued for breach of confidentiality or even fiduciary duty.
Under law, fiduciary duty is a relationship of confidence and trust between you, your business and your clients. Issues can arise if your client believes you are not acting within their best interests.
Having the right insurance cover for breach of duty is particularly important in industries such as accountancy, architecture, quantity surveying or estate agency.