It’s common for business owners to use their personal vehicles to run a quick errand that is business related, or to ask an employee to do the same.  If you have a collision and get sued, it’s possible that neither your personal insurance nor your business insurance will cover you under these circumstances: the business insurer will say that the vehicle is not covered; the personal insurer will say that business pursuits are not covered.

With respect to leased, rented, hired, and borrowed vehicles, clearly your personal insurance will not cover you; your business insurer might not either as it will argue that the vehicle was not scheduled (listed) on the policy.