I always buy it when traveling abroad, primarily for health/hospitalization. Medicare and most private insurance does not cover issues abroad.

Trying to get cancellation refunds through separate travel insurance policies is not easy; they will fight you tooth and nail. I typically choose a cancellation benefit for about $40 when booking through an online ticket broker. Note: this is only if the airline cancels your flight; if one cancels for reasons of their own it's tough luck.

"The whole problem with the world is that fools & fanatics are always so certain of themselves, and wiser people so full of doubt" Bertrand Russell