People buy travel insurance to mitigate travel-related risks, so the reason for buying varies depending on what your risks are. The major ones to consider are usually:
 

Trip Cancellation Insurance

Flights, Hotels, and even car-rentals have stringent cancellation policies and the last thing you want is to forfeit the trip and lose money because you or someone else on the trip is unable to travel because of illness, injury or even death.
However, if you are driving to another state in your own car and staying with friends or family this risk is very low.
 

Travel Medical Insurance

Medical treatment can be very expensive, even something like food-poisoning can cost you thousands of dollars. Not to mention injuries where you need to be evacuated.
 
If you are traveling domestically, check the extent of your medical coverage — in most cases, you may be covered. However, if you are going skiing or doing other sports you may not have adequate cover.
 

Loss, Theft of Personal Possessions

If you are not traveling with expensive items, then you can overlook this cover. However, if you are traveling with business machines like expensive laptops, you will need travel insurance. It is never advisable to travel with expensive jewelry because travel insurance has limitations on how much they’ll pay out for personal possessions.
 

Loss and/or Misplaced Baggage

If you are on a short trip with hand-baggage only this is not an issue and long as you are not carrying expensive items with you in the hand-baggage.
 
If you do have baggage, especially expensive sports equipment like ski gear or golfing equip; travel insurance is a must.
 
The above considerations may apply for short domestic trips but longer trips, especially international ones, would definitely require travel insurance. A good travel insurance of course, provides you with much more protection than what’s listed above, so know what you are risking when traveling without adequate travel cover.
 
In some instances, you’ll require insurance for domestic trips as well, like business or sporting trips where the risks listed above are a reality.