My Mom and Dad did this. They bought a second-to-die whole life policy on themselves, then stuck the policy itself into an ILIT, which is owned by a trust, of which my siblings and I are beneficiaries.
The annual premium bought about $41 of face value per dollar; they started the policy in their late 50's or early 60's.
The insurance agent demonstrated that my parents would only have to pay the premiums for 10, maybe 12 years, then the policy would be "paid up" (i.e., dividends would be enough to pay the premium).
I think my parents paid the premium for more like 15 or 20 years (gee, the agent was too optimistic - color me not surprised), and the face value of the policy is maybe half of what they would have made just investing the money. There was also the lawyers fees for setting up the trust and the hassle of conveying the policy into the trust and then paying the policy via the trust for the past dozen years or so.
The agent also didn't point out to us that the policy had been paid up for the past three or four years or so, and our annual premium was not really buying us much of anything beyond perhaps a nice signed holiday card from the agent.
It does provide relatively quick (think ~3 months; it's not the next day as the insurance people claim), unencumbered tax-free cash, which we could use to pay estate taxes, so that feature is moderately nice. If you need it. With the estate tax exemption amount, my Mom estate didn't owe a penny of estate taxes. My Dad is still alive and kicking, but his estate is looking like it's in the same situation unless the government lowers the exemption amount. Which they well may at some point.
So maybe good idea in theory but not so much in practice.