Is only one summary task allowed for cost schedules and work schedules?

Developers
1

In IFC4, there is this statement:

There is always a summary cost item as the root item of the tree representing the cost item nesting. Subsequent instances of IfcCostItem are assigned to the summary cost item using IfcRelNests. The summary cost item itself is assigned to IfcCostSchedule through the IfcRelAssignsToControl relationship.

Is more than one summary cost item allowed?

Option 1:

  • Cost Schedule
    • Summary Cost Item
      • Nested Cost Item 1
      • Nested Cost Item 2
      • Nested Cost Item …
        • Nested Cost Item …

Option 2:

  • Cost Schedule
    • Summary Cost Item 1
      • Nested Cost Item 1
      • Nested Cost Item 2
      • Nested Cost Item …
        • Nested Cost Item …
    • Summary Cost Item 2
      • Nested Cost Item 1
      • Nested Cost Item 2
      • Nested Cost Item …
        • Nested Cost Item …

If it is option 1, what is the technical reasoning to have this summary task, to the point that it is even recommended that this summary task is “hidden” from the user?