I know this response is a month old, but Premier and newer TiVos do actually have a manual
power down state where the system is inactive unless a recording is in progress or scheduled (so you can't skip backwards 30 minute from when you turned it back on, which is the only disadvantage I'm aware of). Roamio actually has selectable power saving. It will not affect scheduled recordings, and IMO is a worthwhile thing to keep enabled.