I don't normally change development to adjust. I've found that normal film contrast/development works well for me in almost every situation. I simply make adjustments and or burn & dodge when printing instead.
I'm confused by the initial question. Then again, it's derby day....
There are two common meanings for the word "contrast".
One type of contrast just refers to the difference between the darkest and lightest parts of the scene - the more the difference, the higher the contrast.
A slight refinement of that description refers only to those parts of the scene where important detail lies - i.e. detailed shadows and detailed highlights.
Some might refer to this as macro contrast. Others would refer to this as something akin to dynamic range.
The other type of contrast refers to the difference between adjacent tones of dark and light in the details of the scene. The greater the difference, the more contrasty those details appear.
Many would refer to this as local contrast or micro contrast.
The quality of light determines the local contrast in the scene.
What follows assumes you are using black and white negative film.
When I am making decisions about exposure and development:
1) the macro contrast is quite determinative of exposure, in that I need to be sure that there is enough exposure for the shadows, but would prefer that the highlights not be over-exposed too much. Usually, the films I use can handle a lot of that though, so it isn't unusual for me to rely on manipulations in the printing darkroom to deal with that. In relatively less common circumstances, the macro contrast of the scene is very small, so I have to depend on the print darkroom to brighten the highlights;
2) the micro contrast influences my development choices, because development controls vary the slope or gamma of the exposure and density response. Increasing development has a similar effect as increasing the contrast or "hardness" of the light on the scene. That development increase may also be used to increase the macro contrast, in situations where the dynamic range in the scene warrants it.
I can go and explain this but it's far easier to go outside yourself and see it.
Have someone stand in front of you in a bright sunny day. Look at the person's face. Notice how nose casts shadow on his/her face. See how much forehead reflects the light. Also notice, the darkness/shadow the chin makes on his/her neck. Make a mental note of the difference in brightness in these area. Or better yet, take a photograph of this.
Then do the same in bright but cloudy day. Then do the same in heavily clouded day. Or, do it in shaded area.... not directly lit.
OR... if you must do this with landscape, pick a subject, pick a camera position and do the same.
You'll notice, more clouded the sky is, the difference gets smaller and smaller.... Remember, the difference of the light level between bright and dark IS the contrast.
Maybe another tack...
The old Kodak recommendation was simply, "If your pictures are consistently too contrasty, reduce development time; if they are consistently too soft, increase development time."
With roll film it is almost impossible to not have scenes of different contrast on one roll unless you use dedicated backs or camera bodies. The thing you want to achieve is a "standard" developing time that allows you to be able to print all those different-contrast scenes on the grades of paper available to you.
When I shoot roll film (which is rarely these days) I like to find a developing time that allows me to print a "normal" scene (think hazy sunlight with open shadows) on grade 3. Then I have enough leeway for more and less contrasty scenes.
You do need to develop a sense of how contrasty the lighting is (soft vs. hard as mentioned above) and where to expose, but that's pretty basic. I recommend to in-camera meter users to use the meter's reading for all cases except when the subject is contrasty. In that case, the meter has a tendency to underexpose the shadows, so open up a stop (or use the +1 stop exposure compensation) for contrasty scenes.
Do that and find a good standard developing time for your style and type of work and you'll be just fine. I'd start with the manufacturer's recommended developing time and then alter that as needed, using "If your pictures are consistently too contrasty, reduce development time; if they are consistently too soft, increase development time" as a guideline.
Thanks for all the helpful info. I will explore these posts further!