PLUS: You can get MicroSD card file system corruption if not using industrial grade MicroSD cards - especially when losing the power...
This is why you have to unmount USB drives, if you pull the drive while data is still in cache would also create problems. The difference is when copying files to the drives, it's sequential, you may lose a file or two. When it's the OS using it as the main drive there are loads of write operations going on.
At least it's easier to add battery backup to a Pi then most other computers.
Well I lost some to power failure, and they all had ext4 on it. Anecdotal I know, but I'll be avoiding RPi for anything that needs to persist data in the future.