Dark data is the stuff companies store but rarely use—60 to 80% of their data...

https://romeo-wiki.win/index.php/How_Do_I_Deal_with_Old_Media_Assets_and_Temp_Files_at_Scale%3F

Dark data is the stuff companies store but rarely use—60 to 80% of their data sits inactive. It matters because holding onto this unused data can cost businesses millions each year, often around $2.5 million in wasted storage and management expenses