Now, I've committed to High Sierra. However, I am a creature of habit and have been routinely using DiskWarrior to check/repair the directory. I think I have only used DW in anger twice to recover a hard drive, once back in OS 8.6 days to recover a system, and once to recover a data only drive that was on it's way to failing.
Often enough for me to keep buying the upgrades. I still use TechTool Pro, too. However, it was mainly to optimize drives and TechTool says not to do that to SSDs. Again, I've kept it up-to-date.
Micromat (TechTool Pro), Prosoft Engineering (Drive Genius), and Apple computer are all in agreement that optimizing files and/or volumes on SSDs is not a good thing to do as there is a risk of reducing drive life and is counterproductive on drives formatted APFS where the location of data on the drive is intentionally randomized. In fact data in multiple APFS Volumes is intermingled on the solid state media.
I still have TechTool Pro and Drive Genius and keep them up to date, but I don't remember the last time I used either "in anger" (thanks freelance I really like that phraseology) if for no other reason than my Time Machine drives still have to be formatted Mac OS Extended. If Mojave supports Time Machine on APFS. OWC's SoftRAID is working on APFS for RAID 0, 1, 2, 5 and when that happens my last possible rationale for updating either will be gone.
