Rebuilding Mac Photo libraries in Powerphotos from iPhoto librari

I’ve discovered that if I drag and drop an older iPhoto library, ‘Package contents’ into a newly created Photolibrary in the Powerphotos window, that a photo library is created with the CORRECT dates for the photos.

This seems a viable method but does anyone know why Powerphotos would recommend their ‘Migration of iPhoto library approach ?