The way it was explained to me (by the rental car company), if there is an accident (or damage) the rental car company collects the damages directly from you and then you get reimbursed (or not) by your car insurance company. That would perhaps be a pain, but not a big deal to most of us who have credit cards or checking accounts that could cover most accidents.
I've always thought the insurance "waiver" was a racket. I never take it as I believe it's mostly a "profit center" for the rental car companies.
Now, I assume that using your own insurance company would include what ever deductible you usually would incur. Whether you could use your CC company to cover that deductible, I do not know. Fortunately, never had to deal with such an eventuality myself. YMMV