Um, just to expand slightly on the above. The question of primary relevance to this thread is not "when might I want to run such-and-such type of scan?" but rather "when might I want to auto power-down at the end of such a scan?". I posit that you are more likely to want to power down on completion of a boot-time scan than under any other type. Why? Well ...
A full scan, whether at boot time or otherwise, typically takes some hours to conclude. At least when running a NON-boot scan you can use the machine for other purposes and let the scan do its thing in the background. So you could well be attendant at the computer while it is going on and, imporantly, on the completion of the scan. By contrast, when a boot-time scan is running, you can do nothing with the machine until it completes its thing which, as I say, may be some hours down the road. I am unlikely to be sitting in front of it all that time watching the % completion button tick over. I don't mind reviewing a completed scan log. But if I set the thing going for a boot time scan (because yes it found threats when last scanned normally), and then I set off for the office while it is chundering away, I would rather not leave it on and idle on conclusion pending my return home.
