My real question is: What is this particular tab doing?
My understanding of the calibration tab is that it allows LR to use a DNG profile to 'normalise' each camera's output back to a 'standard', or predetermined, rendition. In a similar way ICC camera profiles work in other raw converters or printer profiles correct for different papers and inks<a gross simplification of how ICC profiles work, but probably helpful enough here>.
It's possible to build custom camera profiles fairly easily via applications like X-Rite Passport, DNG profile editor and QP card, these allow individual camera profiles to be built on a per-camera body method that can help some people get the best from their cameras. (This subject has been discussed in great detail many times before on LL)
The complication is that the DNG profiles can also be used to give specific 'looks' eg when matching the in-camera JPG picture styles most cameras offer as well as just standardising the output.
is there something going on under the hood in ACR that is much more complex?
I think that the DNG profile creation software has more sophistication than just using the options available in the camera calibration tab.
Hopefully someone with more knowledge can confirm or deny that assumption.
Below I’ve attached some screen grabs to show what one of VSCO’s film emulation presets looks like. If it doesn’t show up, it reads // Agfa Scala 200X, in the Profile section, and it has made two small adjustments in Red and Blue Channel Saturation. I’ve also attached the various film Profiles that VSCO includes.
It looks like VSCO are using a DNG profile to create their 'look'. Curious as that would preclude being able to compensate for individual camera characteristics unless they offered each film preset for every camera which doesn't seem to be the case, so the same preset will give a different look dependent on camera.
I'd guess that VSCO would say that their film type is far more significant than the minor differences between cameras, or that the DNG profile creation software allows a better range of options for fine tuning output, more likely they think it's harder to reverse engineer and copy than using a normal preset.
Other than that, the controls within the tab are just another set of tools at one's disposal that can change the rendition of the image. It's settings can be saved into a user preset, just like any other control.
Personally I'm no fan of pre-made presets that impose other people's looks or styles.
I do create custom DNG profiles for my cameras, my own preference is for QP card ones, and I'll sometimes create a special one for unusual situations. I keep a mini CC24 in my camera bag for such eventualities. I then use a user made preset for each of my cameras that applies the appropriate DNG custom profiles and my preferred sharpening settings for use when importing. That gets images into LR at a good set of defaults that I like to work from.