From Bushwalk Australia
An attribute of many high quality double-skinned hiking tents. An integral pitch design means that both the tent fly and the inner-tent can be left connected and pitched simultaneously. This allows for rapid pitching, which can be advantageous in poor weather.
Many such tents also allow other setup options, such as pitching the fly on its own as a quick and lightweight shelter.
Some designs may also provide for the inner tent to be pitched alone in warm conditions as protection against mosquitoes and other insects (a "bug shelter").