How long will Computer Forensic Standards Last?

How long will Computer Forensic Standards Last?A police officer switching ON a device that is already switched OFF at a potental crime scene should be an absolute no-no, according to Forensic bibles, case law etc. Indeed, even the Police's official release version of ACPO Guidelines categorically states for Crime Scenes Page 8/66: "• Do not, in any circumstances, switch the computer on."Why does