While these tents cannot be used in instances such as dungeons and raids, they can be used anywhere in the open world: garrison invasions, trapping elite beasts, the group Apexis quests, or any other non-instanced activity. You can only carry 5 of each type of tent at a time, but they're Battle.net Account Bound and there are 21 different types of tents available. That means you can carry a potential 105 tents per character ... which makes their Unique limitations somewhat pointless.
These tents aren't the most powerful thing in the world, but they're neat items and might provide the boost your group needs to achieve Gold in a garrison invasion. If you have a Barn producing leather, you might as well use some of it for a solid questing buff.