AWS Image creation with "no-reboot" option - what is meant by "file system integrity"?

In AWS, when creating an EBS image of an EC2 drive, there is an option called "no reboot", which allows you to create it without rebooting the machine. When using this option, there is a warning:

When enabled, Amazon EC2 does not shut down the instance
before creating the image. When this option is used, file
system integrity on the created image cannot be guaranteed.

What exactly is meant by this warning?

Is it:

1) All writes to the are disk unsafe (including writes to log files), because there is a chance that the filesystem itself in the created image is corrupted.

Or:

2) Writes to the disk are not guaranteed to be copied to the image in a consistent manner. For instance, if your instance writes to file A before file B during image creation, and File A is necessary for File B to be correct, you might not have file A in the created image.

Or is it something different entirely?