Metric Insights is designed to accomodate many generations of Category/Subcategory hierachy but only 10 offspring per parent.  Users must confirm to established Category hierarchy limits in order to avoid an aderse effect on  performance.

1. A parent Category at any level may only have only 10 Subcategories (children); i.e., horizontally
2. The number of "generations"  is limited (vertically) only by the convenience of working with the main grid of Categories;
   1. There is no pagination for the List Page display because the drag and drop  capability that is used to sort Category order would not be functional on a long page.
   2.  If an excessive number of Categories; e.g. , more than 1000, the grid displays will be too long and unusable.
3. A large number of Categories can negatively affect the overall performance of the Metric Insights system, since many Permissions and access rights must be calculated during request processing.

See Create a Category and Category Privileges:  Release 6.2.1 and beyond

1.  Original Parent Category

2.  Horizontal limit: 10 children

3. Vertical Generations:  no limit