Ralph, I understand and I trust your expertise. However, for me, altering contrast is a lot about changing how highlights look in comparison to BOTH shadows and mid-tones. As I slow down agitation and increase agitation intervals to about 3 or 4 minutes, even 5 minutes in extreme contrast situations, I maintain fantastic density in the areas of the negative that are more conducive to develop thanks to time, i.e. tones that are closer to shadows, all while I 'calm down' the intensity in the highlights, which to me seem to be more affected by agitation than anything else (i.e. contrast). As I slow agitation cycles down and spread them out farther, I also adjust total development time, but I view that as a consequence of slowing agitation down, not as a means in and of itself.
What results is a perfect negative almost every time, where I spend a very small amount of time tweaking the prints in the darkroom; most of my prints are very close to straight at Grade 2. I'm not saying you can't achieve this any other way, of course! But for me this approach gives me the consistency and the degree of control that I need to get my negatives in tune with my paper of choice.