When you start carrying trade related people (like employees or customers) and goods or equipment in the car you should seriously consider adding business use. Liability requirements of a trade and a person are generally different. For example, the customers who are injured in a traffic accident in your car can sue you or choose to sue the company. This would cause serious headaches for you. So, you need to get it right.
Another important point to look at is how the car is insured currently. Some automobiles may have pleasure only policies (because they are cheaper) that don’t include any commercial use or even commute depending on the wording. You must make sure that you have a standard policy (not leisure only). Standard ones would have more provisions and certain level of flexibility.
The last point to look at is if any business mileage declared for tax purposes. If that is the case, it should have this element in there. You cannot tell the taxman that you are running errands in it and not tell the carrier. People may worry that it will increase vehicle insurance rates but additional charges may be negligible. At least you can get quotes for it and see the difference.
Still depending on where you live, the automobile insurer you are with and the wordings, there are various automatic business uses allowed with private auto policies. For example, it was ruled in one state (cannot remember which one) that doing pizza delivery with a private vehicle would not require having business auto insurance. You can ask these things to the agent or broker and they will be able to check it for you.
If you have a typical coverage with no restrictions (as mentioned above) and you are a self-employed accountant who occasionally visit client’s premises but don’t carry any passengers or goods you probably don’t need to worry about it much. Running an errand relating to a trade once in a blue moon shouldn’t worry underwriters as long as the above point are watched.
At times, people cannot separate work from pleasure. For example, you may be going somewhere to have a meal but you may drop to see a client on the way. It is difficult to differentiate which is what in such circumstances and you cannot be worried about it each time. If you do, it is better to have the appropriate endorsement on the schedule even it means paying a little bit more premium.