Me, I'm joining the new user contingent in a sense and not upgrading either TTP or DW until I must, and that may be several paid upgrades from now. (The availability of both utilities via d/l rather than snail mail as was once the case makes that position even more tenable: as long as you've got a bootable volume you can get the latest version of either utility within minutes of your needing it.)
The problem is that you may not be able to access those apps if your data are so damaged that normal operations are impossible.
That said, I have noticed that Disk Warrior rarely finds anything amiss after Leopard. Snowy was very, very stable, and El Cap is at least its equal (as was Yosemite) in that regard. I run DW once in awhile for kicks. I never used Lion, Mountain Lion, or Mavericks so I can't comment about them.
I have been upgrading TechTool Pro ever since I first purchased it, and that of course is/was a wise move, given that I use it on a regular basis. And I have used it through all the "intervening" OS versions that jchuzi mentioned. As I stated earlier, believing that the Mac OS is going to keep things "lean, mean, and clean" is asking for trouble. If one wants to remain in reactive mode when trouble arises, that's their choice. I am staying with the crowd that is proactive, and thus staying in front of any potential issues. I practice that same philosophy in other aspects of life, not just with computers and technology. And, of course, it fits perfectly with my KISS philosophy: Keep It Simple Stupid.
As for the possible inability to access such apps due to data being so damaged, that is precisely one reason why using tools such as TechTool Pro, Disk Warrior, and Onyx goes a long, long way towards minimizing and/or eliminating such a catastrophic event (and other problems too). And, of course, having a recent, clean backup is definitely prudent.
Nope, I'm remaining with the proactive crowd, and I'm not going to stick my head in the sand like the proverbial ostrich and hope for the best. I'm going to be in front of such issues as much as possible. And, that applies to just about anything I do.
Regarding these tools not finding anything amiss, yes, in most instances, that is what I am also seeing. But, the times when I have needed assistance from such tools have been life savers. And, in 99% of those cases, the "fix" was not difficult at all. The OS was useless in trying to resolve the issue. About the only times such tools (and anything else) could not help was 1) when one of my hard drives could not be repaired at all, and 2) when the motherboard on my vintage 2006 MacPro "died". In both issues, it was not due to any mismanagement, nor reliance on the OS. On the contrary, both products had been in use for quite some time. The hard drive issue was due to normal wear and tear, as it died after about 6 years of use. Not sure why the motherboard died in the MacPro, but the machine became a dinosaur anyway with the advent of one of the "newer" versions of the Mac OS (can't remember exactly which one). But, I did get a lot of trouble free, productive use out of both devices, and using tools like Onyx and TechTool Pro (along with my other proactive tasks) went a long, long way in keeping things "lean, clean, and mean".
