You never think insurance is necessary until you need to file a claim,at which point its too late.
I got very sick 3 weeks prior to a cruise and had to cancel. Thank God I had the insurance,got a full refund.
Interestingly,if you are on medication of any kind,insurance companies consider you to have a preexisting condition and may deny a claim,unless you get a policy that covers preexisting conditions. Usually this coverage has to be booked soon after initial deposit. The company I use requires I buy ins within 15 days of booking for example.
Shop around as coverage and rates vary significantly.