I would imagine the advice was given to crop in ACR vs PE because edits within ACR would be non-destrctive vs PE which would be editing a JPEG in a destructive manner. I don't use either tool directly but this would be my assumption.

For example, once you crop and save in Photoshop Elements, the image is overwritten and the cropped portion of the image lost(unless you Save As and create multiple files). In a tool like Adobe Camera RAW your edits are non-destructive to the original RAW File and saved in a separate file with the extension of XMP. It is only upon export of the edits that you will create a new file that is cropped(with any other ACR adjustments), but your RAW file remains unchanged.

See: Why is Camera RAW changing my original raw file?

I would imagine the advice was given to crop in ACR vs PE because edits within ACR would be non-destrctive vs PE which would be editing a JPEG in a destructive manner. I don't use either tool directly but this would be my assumption.

For example, once you crop and save in Photoshop Elements, the image is overwritten and the cropped portion of the image lost(unless you Save As and create multiple files). In a tool like Adobe Camera RAW your edits are non-destructive to the original RAW File and saved in a separate file with the extension of XMP. It is only upon export of the edits that you will create a new file that is cropped(with any other ACR adjustments), but your RAW file remains unchanged.

See: Why is Camera RAW changing my original raw file?