AH has skins options. You select an aircraft in the hangar, and there is a drop-box at the top. From there you can choose different skins to fly in. If you do not have the check box enabled, you will not download new skins.
On one hand, it takes up bandwidth, and can make you lag. On the other hand, it is one of the more reliable ways to get new skins when they are released.
Note that it does not always download skins, only when the server has new ones that you have not yet downloaded.