Before anyone chases changes in contrast at the negative it is important to remember/understand that negatives are normally just an intermediate medium. Proper contrast should normally be judged by the output/print.
Increasing time, agitation, or temperature for film development will increase the steepness of the film curve. When that steeper curve is printed the mid tones are going to be snappier but some highlight and shadow detail will not print unless you dodge or burn. The inverse is true also.
Experience has taught me that most of what I thought were contrast problems, are actually exposure problems. The problem for me is not normally the steepness of the film curve, but where the subjects I want to print land on the film curve too far apart.
To get the subjects closer to each other on paper, I can dodge and burn in the enlarger or light the scene in front of the camera differently.
The classic example of this is a backlit portrait; sunset behind your subject, very little light on your subjects face. In this situation the contrast in the scene is huge. The steepness of a normally developed film curve may be right for both subjects they are just too far apart on the film curve. Adding artificial light on the person or doing dodge and burn at the print can be used to place both subjects on the paper.
Adjusting the film's contrast allows you to print more or less of the whole scene but it does not help place a dark face and the sunset where you want them on paper.