If your business involves giving advice and using professional skills to aid your clients, then you might need professional liability coverage to protect you should your client claim that you have made a mistake in your advice or been negligent in your work and your client has suffered losses as a result.
Mistakes do happen, however careful you are, and sometimes clients can just look for someone to blame if things go wrong for them. If a client has lost money and thinks they can get it back by blaming someone else (i.e. you) then you may be faced with a claim for compensation through the courts.