I have always unplugged my TV when going on vacation to avoid damage by power surges, lightning strikes, etc. When I had TV via cable , I always left the PVR plugged in as a necessity for recording. I now have Ignite and I suspect it would be OK to unplug the set top box by the TV while I'm away. Is there any reason why I should not?
Since the recordings are in the cloud and since they get recorded if there is a power failure at your home, I also would have guessed that the box doesn't need to be plugged in for programming to be recorded. However, even with the older digital cable, the system did occasionally check to see if you had your STBs hooked up and deactivated those boxes after a period of time if they were not connected. I believe it was something like 3 weeks. Perhaps this is what @RogersAndy is referring to? Also, if you had 3 boxes, would all 3 need to remain connected? These Ignite boxes use almost no power, so from a power saving standpoint the savings are minimal, however, as you state, there is almost always a concern from power surges.
I used to unplug my digital boxes when on vacation too, however, I found that they often didn't reboot properly when I came back from vacation and often required either many attempts to reboot, or several calls for reauthorization because the boxes are owned and "appeared" to be "dead", so now I don't do that any more... (In my case it was a major pain to ask for second level to get the boxes active again).
I have 3 PVRs and one regular STB and previously unplugged all but one. My PVRs plugged into a UPS to preclude head crashes, etc, which also provides surge protection. However, again, the Ignite boxes don't have an iHDD, so there is not as much concern. Since the Ignite boxes are rentals, if the box goes bad, you should be able to easily swap it out?