I can understand Picard's decision to perform an engramatic purge on the girl Data saved so that she would not remember anything vis a vis The Enterprise. But I found it to be sad that she would have no memory of being saved by Data, whom she regarded as her hero and with whom she had formed an emotional bond. Also, practically, could there not be some benefit to the inhabitants of that world of having some idea of how they were saved, in case the problem reoccurs? To be clear, I'm not complaining about the writing or the episode or anything like that. Picard's decision was believable. It was just sad. Good episode.