What is the camping tent used for?

Solution 1:

From this unofficial DayZ Wiki:

Tents are items that offer a source of storage players. They do not save from server to server but on the originating server they were deployed on. Deployed tents cannot be stolen, however the items inside can be.

So, tents stay on the server they were pitched on and do not follow you to other servers.

It also says the Save command "properly saves a tent although there still is a chance that a server will eat your tent no matter what."

More info here.

Solution 2:

The tents are used for storage, they save through server restarts. You use the save option to save the contents.