I am not so sure that pet insurance is really useful for preventative stuff like shots, spay/neuter, etc. You would be better off saving up for that stuff and scheduling it on your own terms.
However, having pet insurance for Kiwi for emergencies gives me peace of mind. I know that if something happened to her, I wouldn't have to worry about vet bills, I could get her the care she needed and submit the bills to the insurance and get reimbursed. I think a lot of us would have a hard time spending thousands of dollars that we wouldn't be able to get back.
Kiwi recently went through alot of testing for liver shunt, including a liver biopsy. Her insurance, Embrace Pet Insurance, paid me back for every cent (minus the deductible). They cover all genetic illnesses! I spent over $1500in vet bills and they sent me a check in two weeks for $1200. And they even followed up afterwards and asked me if Kiwi had recovered well from surgery!