If you are offering professional services & advice (including free advice), it's a good idea to take out Professional Indemnity cover to protect your business. If the services/advice you gave transpired to be negligent, and a third party subsequently suffered loss or damage, they could make a claim against you.
If you don't have the correct Professional Indemnity cover in place and a claim is made against you, you will have to pay any compensations costs and legal fees from your own pocket.
You may also be required to take out PI cover by law or in line with a trade association/regulatory body.