The CIM_AggregatePExtent class provides summary information about the addressable logical blocks which are in the same storage ...

The CIM_AggregatePExtent class provides summary information about the addressable logical blocks which are in the same storage redundancy group and reside on the same physical media. This is an alternative grouping for physical extents, when only summary information is needed or when automatic configuration is used. Automatic configuration can result in thousands of physical extents being defined. There is no value in modeling the individual extents.  So, the CIM_AggregatePExtent object was defined.