As for it being less important, if either one takes excellent, excellent care of their machines, or does not care about such issues and just replaces either their Mac or the drive, then yes, there is no need for such a product. That's not for me.
The issue is not whether one is a ‘responsible’ computer owner by the exclusive virtue of running any or all system utilities one can bring to bear, but whether such behavior is necessary. It can be argued that over the years the changes/improvements in Mac OS X have markedly reduced the need to apply such utilities, as exemplified by the many users who worked their way through the lifespan of successive Macs without ever running into a problem that required the ministrations of a 3rd party utility. In this scenario, the utilities monitor things just fine, but rarely if ever have to actually
do anything. I would make an exception for the preventive value of things like SMART monitoring, but that particular option isn’t without its foibles either. And having ample backups renders the occasional hardware hiccup moot anyway.
Part of that depends on how dedicated the individual is to keeping things in good to excellent order with their machines. Also, it is a mistake to think that the improvements in the OS will minimize/alleviate the need for products such as TechTool Pro and/or Disk Warrior. Case in point: I own a 2013 Toyota Camry. Like Macs, they are built rock solid, with continuing improvements on that reputation. But, I am definitely not going to only reply on the technology of that vehicle to keep things running smoothly. That would be foolish. Just like with my Macs, I am proactive in doing some things for the vehicle that go beyond what the maintenance schedule says. Three simple and cost effective things are 1) changing the Cabin Air Filter myself, 2) changing the Air Filter myself, and 3) checking tire pressure myself. Sure, for #1 and #2, there are mileage milestones associated with each of those, and for #3, the particular model I own has a feature that lets me know when tire pressure is low. But, I would much rather get in front of such simple things myself.
So, similarly with my Macs, I use products like Onyx and TechTool Pro to do things beyond what the OS can do. And regarding backups, I first go through my disk maintenance/cleanup/repair routines, and then do my backups. That insures the backups are lean and clean. Another case in point is the recent "debacle" I encountered while booting to Safe Mode on my Mac MIni (running OS 10.11.3). Issues arose from that event which the OS could not resolve. But, Onyx came to the rescue and resolved the issues in an effective, conclusive manner.
What it comes down to is a matter of choice. Like other things, one can solely rely on technology to cure issues, or one can be proactive and do some additional, useful, proven tasks on their own to
augment what technology does. Myself, I take that latter approach, and am glad I do. As it is, I have been following such practices for so, so long (even when I had my Apple IIE, Apple IIGS, and all the prior Macs I have owned) that is part of my DNA.
Finally, so many individuals in society want to use as many short cuts as they can, no matter how potentially harmful they are (without taking precautions). Yes, my disk cleanup/maintenance/repair and backup tasks do take time, but I always do it while I am doing other, productive, non-computer tasks, and thus I am not waisting time. It seems like the concept of multi-tasking is missing these days.
