Your insurance company could choose to sue a third party to recover the amount of a claim they paid if the loss was caused by that third party. This is called subrogation.
Some contractual agreements, including some facility rental agreements, require you to waive your right of subrogation (and therefore your insurance company’s rights) against them in the event of a claim.
Many, but not all, general liability policies allow you to waive your rights of subrogation as long as it is required by written contract.
There is an additional cost to have the endorsement added to your policy.