The advantage I see with page group is that we can directly refer to an item in the list where as in pagelist we need to iterate through the list items. I think we need to created indexes for list type properties.
Right Click on a single value property in the embedded list type property and click "Optimize for reporting", pega will automatically create a declare index rule, an index class and a table in database.
Page type properties(non scalar once) will be stored as part of BLOB column in the work object table so reporting on these columns is not optimized.
To enable reporting, we have to create declare index for these properties. Once this is done, Pega creates an index table with columns same as the properties in the page and runs a query(in the background) against all the work objects to populate this newly created index table.