Usually data losses may only be possible in cases of faulty hardware or unclean shutdowns (sudden power outages, heat protection kick-ins, BSODs, etc.). But many programs are aware of that (all programs which are designed with safety in mind) so, for example, they don't just overwrite data in place: they create a new file, write data there, flush cache to ensure it's written, then remove the old file.
Without this checkbox, if failure occurs at any point, you'll always have at least the old version of data.
When box is checked (without buffer flushing), in case of power failure or sudden reset, data losses may be vast and uncontrollable, you may even lose data unrelated to files being written because file-system updates occur with same principles. You may even completely lose all data on the volume, if failure occurs in an especially unfortunate time. Even worse: in some cases, you may lose data on clean shutdown/reboot, if drive doesn't flush cache on its own before reset.
Because of that, disabling buffer flushing without independent power supply for the drive is playing with fire. If you're using SSD for non-original data (caches, mirroring of slower storage for fast access, non-original program files, Steam or other means of games installs, etc), and willing to risk it (though in case of steam, beware of loosing savefiles, depending on where games put them), you may check that. But expect catastrophic failures occasionally (especially in case of unclean shutdown/unmount), and probably just reformat and re-fill the drive with data in such a case, instead of trying to recover.
Also, ensure performance gains are real and significant. Because maybe the first test just tries to flush after each write, which will indeed cripple performance, but barely this is done by any widely used application at all.
related:
blogs.msdn.microsoft.com/oldnewthing
Sandisk ExpressCache manual:
Some other forums
Best Answer
You are likely suffering from the Force Unit Access type for your write operations. While it is meant to maintain durability for all writes, there might be regressions especially with NVMe drives and certain device / firmware / driver combinations. The PCMark FAQ is describing something very similar:
If the NVMe drive is part of your Dell order and the system is still under warranty, ultimately contact Dell support about this issue. They might be able to supply you with newer drivers and / or firmware for this drive which might resolve your problem.
Otherwise, you might want to try OCZ RevoDrive 400 drivers (The RD400 is essentially a retail version of the Toshiba XG3) instead of whatever's pre-shipped with your image. Also, enabling write caching for the drive (if disabled) might speed up matters.