By using the same exposure and contrast and sharpness and … adjustment tools, I get better at using those tools and avoid the need to learn a duplicate set of tools.
If I'm going to dive-in and pull-at-the-curve to up-the-contrast for that part of the image; it's nice to do that with a familiar tool and it's nice not to care what that does to the other parts of the image (because when I get around to selecting what parts will contribute to the final image, they won't be selected).
It's just what I've ended-up doing, I'm not selling anything :-)
I realize that what you describe is SOP for many photographers, but I am convinced that fine tuning and local adjustments are better done on a converted image than a raw file, if IQ is your highest priority. As a test, download a free trial version of Perfect Photo Suite 8.5 and familiarize yourself with some of its modules and tools, which may take some time and effort. You can work with it either as a standalone or a plugin program. Then use it to edit a converted image that has had basic adjustments only applied in Lightroom or whatever integrated raw image editor you normally use. Finally, edit the same raw
file exclusively in Lightroom and output the file to TIFF. Now compare the two. I think you will see the difference. Also, for those who use Lightroom plugins such as Nik and OnOne, those edits are being done on converted, not raw, files, which only serves to make my point. I have no problem with the plugin concept, but people should understand what they are doing. The same can be said of working in Photoshop, but to do it right requires more skill and effort. (PS purists, I salute you.)