This feature makes it easy to assign categories to posts. The categories can then be searched, to find all of the members. In QDL, categories are folders, and anytime something is assigned to a category, a link to it is created inside the category folder. To review all of the items in a category, just go to the folder and view the contents.
If you haven't already used this feature, you don't have any categories to assign, so click the Categories... button, and select the folders you want to use for categories. If you haven't already created them, you can do so now. Folders to be used as categories can be anywhere. Categories you intend to keep to yourself can be created in your Sandbox. Categories that you intend to share with others can be created in your blob, team folder, or elsewhere.
Once you've assigned categories to posts, if you remove those categories from your list, all of the existing posts will still be in the assigned categories. To remove posts from categories you're not using anymore, go to the folders, and cut the links.
To see categories assigned to posts, hold down the Shift key while hovering the mouse over the title.
Category folders have rights just like all folders in QDL. In order to add and remove items from a category, you need at least editor rights. You can also grant reader rights to others, if it would be useful for them to see what's in a category.