A contractor rents a lift or an excavator for a job. At the counter, the rental yard offers a damage waiver for a daily charge. The contractor declines it because "insurance covers it." Then the machine is stolen or damaged, and it turns out the contractor's policy doesn't cover rented equipment, or doesn't cover enough of it.
Rented equipment falls between policies more often than clients expect. The GL usually excludes damage to property in the insured's care, custody or control. The contractors equipment floater may cover rented items only up to a small limit, or not at all.
The short version
Before a client declines a rental damage waiver, confirm the contractors equipment policy covers rented and leased equipment, at a limit high enough for what they rent, and whether it pays the rental company's loss-of-use charges.