The plot thickens a bit on the issue of saving your data according to the inSync reader who wrote this.
Many operating systems, including Windows (in all its various flavors) and MacOS often employ a technique referred to as write-back caching, or “lazy writes.” This means that the OS keeps modified disk data in memory and writes it some time AFTER the application believes it’s written. This is done for performance reasons — to “collect up” and “compress out” duplicate and sequential operations to minimize and speed up the actual writes.
The down side (of course) is that if you have a power failure or “just turn the computer off” (rather than shutting it down), you may lose data. Depending on the method employed, you can have missing files, files that seem to revert to older contents, corrupted files, and/or corrupted disks. This is why Windows runs “check disk” if a system wasn’t shut down properly [Ed- Mac also defaults to this, though you can turn it off].