I find the C modes incredibly useful, and one of the upgrades the S1RII has that I really like is having 5 C modes directly available compared the 3 of the older bodies, and I switch between them daily. Once I have my camera setup the way I want it, I rarely use the P/A/S/M locations on the PASM dial. I do routinely switch between A and M modes, but I use the C modes to do that. C1 for handheld landscape, which means A (aperture set to F8 and ISO set to 80). Also set AF to single area and turn of subject detection. C2 is tripod landscape, so similar to C1, but also disable OIS, turn off hand-held HR,and set it to pin-point AF. C3 is for astro, which means M, with a default 15 second shutter speed, aperture of F2.8, and ISO set to 1600, single are AF. C4 is sports/wildlife, so M (1/1000, wide-open, auto ISO, zone AF, subject detection enabled).
All this really saves me time and keeps me focused on my goal (photography) when I'm out in the field. So if I'm photographing a scene, and some wildlife shows up, I just switch to C4 and start shooting. If I need to, I can also quickly switch to AFC and a continuous drive mode. Quick & easy. As for the S9, I personally would not give up the AF lever or the drive mode dial in order to get C control over those items, but it does make sense that Panasonic choose to do that for that particular body
I also change some of my button mappings between C modes. So yeah, overall, I find the C modes invaluable.
In fact, the lack of C modes is one of the reasons I moved away from Fuji X. Since the X bodies give dial-based control of shutter speed, ISO, and aperture, and since having a C mode override physical dials doesn't make sense, Fuji chooses to not to not have C modes for X bodies. In fact, they do not even have a PASM dial. Some people love this, but I grew to view it as a hindrance.