It really is very specific to how you travel and what your costs/cancellation are. I NEVER get it. My reasoning is:
1. Park tickets. Biggest cost of our trip usually. We can hang onto the vouchers indefinitely if we don't activate them.
2. Airfare. We almost always book on Southwest with points. There is no penalty to change or cancel your flight with points up to 24 hours in advance. So very little risk there.
3. Hotel. We are DVC, so our points would go into holding. There is a risk of losing those.
4. Rental Car. We never prepay so you can cancel at any time with no penalty.
5. Food/Dining. We do not do the dining plan so if we don't go, obviously we aren't out any money for food. I just cancel the ADR's.
6. Experiences. Most things that you prebook and pay in advance for Disney have a 24-48 hour cancellation window. So again, very little risk.
7. Incidental costs. Pretty much all our other trip costs are incidentals and we wouldn't have to pay unless we actually used them (groceries, gas, souvenirs, airport parking, tips, etc).
My DH and I are going on a cruise, leaving tomorrow. Again, I chose not to get the insurance because if we had to cancel last minute, I am out $800 for the cruise. Not a huge amount of money. We travel a lot, so paying $100-$200 for the slight chance we needed the insurance just isn't worth it to us because basically that would really add up and we could just take an extra trip with that money.
That being said, we did take a really big European trip a few years ago that ended up being about $5000 for the two of us and most of it we would not have gotten back if we cancelled. That trip it was worth it for us to pay the $200 for the
trip insurance.