We purchased when we took a couple of grandkids two years ago. The reason we did is because all the grandkids seem to pass around viruses all the time and we didn't want to be stuck with airline tickets and a larger room than DH and I need. When DH and I go to WDW by ourselves, we haven't purchased
trip insurance.
DH and I also bought trip insurance (not the stuff offered through Disney though) when we went to Scotland and Ireland. You just never know what might happen and with the cost of that trip, we just wanted to be covered.
Then, DH and I had a trip planned to Phoenix last month (combination business/pleasure). We didn't purchase trip insurance and, well...you guessed it. DH had an attack of kidney stones two days before we left, had to have them zapped, and missed the trip. The airline company is going to let us use the tickets on another trip that we have one year from date of purchase to schedule. They will decide when we reschedule whether or not to charge us the re-ticketing fee in addition to the difference between the price of old airfare and new airfare we will have to pay. We're keeping copies of all the medical stuff showing dates and treatments.
All that said, we're taking grandaughter, her best friend, son and daughter-in-law in May. We haven't discussed trip insurance, so I think I will bring it up, but I don't think we will this time.
It is cheap peace of mind though.