Just a brief and final reply before I hit the sack. Not theory but practical user experiences.
When Windows proclaimed the device is still in use and the users pulled it out, many have found many files corrupted. hmmm... they were not reading or writing anything. According to them it was idle.
Again I have to emphasise, it may not happen all the time and to everybody. It depends on what processes are running in the background - not only the Window's processes but also the processes initiated by other installed programs, many of which do not close down even after closing the programs. Those may still be reading if not writing. And then even a virus can be reading and writing.
It is always safer to use any workarounds to close all running processes and safely remove the devices rather than taking a chance.
Good night and Good day - as applicable.