Many people use poly tarps when moving. It is great to throw over either a pick up bed or trailer to protect your furnishings from wind and rain. You also are lessening the chances that your things will be cover in dust. Moving is a difficult task but having to clean and repair furnishings when they arrive can take unnecessary time, so using one of these is an ideal solution.
Many times during flooding you will see that a tarp is used for many reasons. Often times when using sand bags to prevent the further wash out of dirt and mud, people will first lay down a tarp and place the sand bags over them to secure them and add extra protection. Also you see them over various building and even cars to prevent further water damage.
If you have outdoor animals a poly tarp also makes great protection for them. Whether building a shelter or covering their dog houses to protect them from rain, they come in handy for our family pets as well.
People also use polyethylene tarps as car covers for added protection. This can be from the rain, snow, and direct sun as well. Many times the cars you find under poly tarps are either being restored or have been restored older cars that can be worth some value. This is also the case after a car accident. Before the vehicle is released from an investigation they will be covered by a tarp so as to prevent further damage.
So as you can see poly tarps have many uses for many different occasions. Having a few on hand is always a very wise thing to do.