The come-ons for insurance are constant and often compelling when you travel. Want to insure your airline ticket? Your cruise? Your luggage, pets, or rental skis? Almost anything can be insured.

It's no surprise that travel insurance is a billion-dollar-a-year business. The industry has recorded steady year-over-year sales increases since Sept. 11, 2001.

But is insurance worth it? That depends.

If you're Adam Creighton, yes. The Cottage Grove, Ore., man purchased travel insurance before leaving for Colombia, where he was building homes for a nonprofit organization - and where he was robbed. "I reported what was stolen - a small gold ring valued at around $250 - and turned in the police report to my travel insurance company along with a receipt for the ring," he says.

The receipt was written in Korean. The travel insurance company translated it, calculated the exchange value of the new ring, and promptly cut him a check.

But, then, if you're Anne Krivicich, travel insurance isn't worth it.

She had planned a once-in-a-lifetime cruise on the Ruby Princess with her husband, Ron. Their 49-day sailing started in Fort Lauderdale, wound around Cape Horn, and then headed north, concluding in Los Angeles. But the Kriviciches never took their dream vacation. Ron Krivicich needed spinal surgery, and even though the couple bought insurance through a company that partnered with the cruise line, they faced a steep loss - $12,133.

Turns out Ron Krivicich's medical condition was preexisting, so a refund was out of the question. Anne Krivicich said she had asked Princess about Ron's back problems. "We were assured that we could cancel for preexisting medical conditions and receive a full refund, minus the cost of the insurance," she says.

The cruise line offered two options: She could either rebook her cruise within a year, or she could receive a transferable voucher through her insurance, good for a future Princess sailing. She says it's unlikely the couple will be able to use either offer.

"On average, most insurance is technically a bad deal," says Jonathan Wu, founder of ValuePenguin.com, an insurance review site. That's particularly true of travel insurance, he says.

Wu reviewed public filings for travel insurance companies and found that many pay a little over half of their premiums toward claims. The rest goes to commissions, administrative costs, taxes, and a profit margin. One filing, which Wu found eye-opening, disclosed that 25 percent of a premium goes to commissions.

In other words, one quarter of every dollar spent got kicked back to a travel agent or website selling the policy.

Those who sell insurance see it differently. Bobbie Rae Murphy, a Maineville, Ohio, travel agent who specializes in cruise and adventure travel, says insurance commissions represent a significant portion of her income, about 5 percent to 7 percent. But she views insurance as a win-win proposition: a source of revenue for her and a valuable product that can save someone's vacation, if not their life savings.

"Accidents happen," she says, "and they can bankrupt you. I counsel my clients so they can understand the potential for issues, then suggest that for just a small amount of money, I can give them peace of mind."

But not all insurance is created equal. Like many well-traveled industry colleagues, Murphy buys an annual plan for herself. Those plans often cover the essentials, including hospitalization, medical evacuation, trip interruptions, and car rentals.

Prospective travelers encounter other types of "insurance" that are probably not worth the trouble. Those can include policies on rental equipment like skis, or rental-car insurance that covers more than vehicle damage.

"For ski rentals, for instance, the most you can lose is the replacement cost of the skis, which may run a few hundred dollars, at most," Wu says. "Under these circumstances, consumers probably aren't getting much value out of insurance, as it's less likely that the risks will cause financial ruin."

Bottom line? A lot of the insurance you're offered while you're traveling - if not most of it - is unnecessary. That's the conclusion of Jonathan Stein, a former insurance adjuster and consumer law attorney in Elk Grove, Calif.

"Most insurance sold to people when they are traveling isn't very helpful," he says. "When you do the math, it ends up being an outrageous premium for very little coverage."

To some observers, the proliferation of insurance products begs for smarter government regulation, if such a thing is possible. After all, there are too many stories of unnecessary policies being pushed on uninformed travelers, not to mention the policies that should have worked but didn't because of a "gotcha" clause.

Until then, remember this when you're on the road: Just because someone offers you insurance, and tells you that you need it, doesn't mean you have to buy it.

Elliott is National Geographic Traveler's reader advocate and author of "How to Be the World's Smartest Traveler."