An additional insured (AI) is reserved for a business name or landlord you want listed on the policy. It is not for other professional providers and/or co-workers.
When you add a landlord or business name to your policy as an AI, you are extending your policy coverages to protect them from any lawsuit that was caused by your negligence.
In other words, if someone slipped in your space of service and broke their arm, the injured person would sue you and the AI. Since the landlord or business name is added as an AI, your insurance policy would protect both you and them in the suit.
There is a $10 charge for each additional insured.