The default behavior of the Studio library catalog tree is to load the next level of categories no matter if they are displayed. This is done to determine if a child category is virtual or not. All occurrences of a category that are not in the primary location in the catalog tree are considered as virtual. Set this property to ALL_EXCEPT_TOP_LEVEL if top level categories should be excluded from pre-loading. It can be useful if there is a huge number of top level categories and if you are sure they are not virtual. In commerce systems where no physical root category exists it must be this way. Moreover, if you are sure there is no virtual category at all you can use the value NONE. If a child category is not pre-loaded, its state is assumed to be non-virtual.