Would you like to add travel insurance to your purchase?

That little pest of a question pops up every time I book a flight, confirm a hotel room or reserve a rental car. It’s become the “Do you want fries with that?” of online travel booking. The difference: Sometimes I buy the fries.

I have never bought travel insurance because instinct has always told me that it’s a bad deal. I rarely pay for hotel rooms, tours or rental cars in advance. I don’t pack designer clothing in my checked luggage. I’m generally healthy, and I have medical insurance that covers me abroad. (It claims to, at least.)

But instinct is a poor way to make decisions about insurance. So with a three-week trip to Asia approaching, I finally decided to figure out whether I should be traveling with insurance and, in general, when it is smart to have it and when is it unnecessary.

Travelers tend to buy insurance if they are more at risk or more likely than the average policyholder to make a claim. In economics that’s called “adverse selection” — but it’s adverse only for the insurance companies. For consumers, it’s just smart. Imagine two people looking at a $100 insurance policy for a two-week trip: One is a 65-year-old heading to India, where he plans to rent a scooter, eat street food and sleep in already reserved five-star hotels every night. The other is a 30-year-old going to London, planning to crash at a friend’s apartment and buy discount theater tickets every night. It’s pretty clear who should buy insurance.

For my own coverage, I looked at packages offered by World Nomads (worldnomads.com), a popular and well-regarded company that provides travel insurance plans online. (If you are buying insurance, try them — or examine the options at insuremytrip.com, a travel insurance search site.)

Generally, travel insurance is sold in packages, combining various categories of coverage. Go through them all, determining what you need and what you don’t, either because you’re not at risk or you’re already covered. If a package doesn’t seem worth it, more customized policies (which you can find through insuremytrip.com, among other sites) offer certain a la carte options. But you may not end up saving that much.

Coverage for my Asia trip through World Nomads would cost me $85 for its standard plan, and $116.40 for slightly more elaborate “explorer” coverage. I looked at each element of their plans — which are similar to most other packages out there — to calculate whether, overall, they might be worth it. Here is a breakdown.

•  Medical: If your regular health insurance doesn’t cover you while abroad, you need some when you travel. Medicare participants and citizens of countries covered by national health services generally fall into this category. Others should check on the specifics of their policies. I have coverage through the Freelancers Insurance Co., which uses the Blue Cross Blue Shield program; my policy states that I’m “assured of receiving care from licensed health care professionals no matter where” I am through the Blue Card Worldwide network.

I went to the Blue Card Worldwide website and was relieved to find many affiliated hospitals listed in the Asian cities I was planning to visit.