'Additional insured' status is most valuable to an upstream party (like an owner or GC) because it:

Explanation

An additional insured endorsement lets the owner or general contractor tender a claim arising out of the subcontractor's work to the subcontractor's insurer and obtain a defense and indemnity under that policy, subject to its terms and limits. (a) is the dangerous reading: risk transfer supplements your own coverage and never excuses it. (b) confuses insurance with cost allocation — adding insureds does not reduce the premium. (c) describes a performance bond, which is a surety obligation rather than an insurance one.