Today's read in of a well-known site says that Fast Startup is a good thing to turn off. I read right through and turned mine off. (normally ON, on W10)
If you dual boot, it seems that it vital to have it OFF.
Long list of reasons to have it off, against a speed advantage I can barely detect with my SSD carrying the OS.
Prior to this, I'd just spent the last half-hour reading posts from folk who are going to Linux or reverting to W7. Me? Well I've done about an hour's serious work since letting Ten barge into my PC a month or so ago. Only an old retired guy could let this state of affairs continue for weeks.