While I've never powered down a single HIVE earned as a witness, I don’t believe there's a necessity for witnesses (or anyone, for that matter) to justify their decisions to power down or explain how those funds are utilized. Witness rewards come in the form of HP; without the option to power down, witnesses would essentially be working for free. The reliability and security of Hive depend on its witnesses, and the rewards they receive are quite modest compared to content rewards. It isn't the responsibility of a witness to financially support projects out of their own pockets.