Why the other party wants it
Imagine your employee is hurt on a general contractor's site and your workers' compensation carrier pays. Without a waiver, the carrier could sue the general contractor to recover what it paid. The general contractor requires a waiver so that your insurance stays your insurance. Landlords ask for the same reason after a fire or water loss.
Blanket or scheduled
A blanket waiver applies automatically to anyone your written contract requires; a scheduled waiver names one party at a time. Blanket forms make certificate requests instant, which is why CoverMatch's comparison flags quotes that include them.
Where it shows up
On the certificate, as a checkbox per policy line and a note in the description of operations citing the endorsement. In the wallet, the policy card lists blanket endorsements the extraction found, and holder requests that tick "waiver of subrogation" are approved automatically when the form is present.