I find his exploration of dark matters to be uniquely stimulating and useful in a variety of thought experiments.
Take The Road, for example. The notion of assessing the probabilities that you'll have enough ammunition to either kill multiple assailants, or alternatively, need to keep the ammunition to kill yourself and your son seems sickening and pointless to explore to some people. Taken seriously and with an open mind, it can invoke serious contemplation of your values, what life means to you, what compassion can really mean, how you take what you have for granted, and more.
As awful as it is to consider, there are real people who have had to make these decisions. That there can be a state of existence in this world where these are pressing matters is simultaneously bewildering and disgusting, yet eye-opening in ways I consider important to living better even outside of that context.
The relentless and ruthless tunnel of gloom and suffering in that book is a useful tool to remind yourself in a vivid way: It's all still here. I'm alive. The trees are green, the rain is clean, the grains are growing for a fall harvest I can still reasonably expect will arrive — life is pretty good. And yet life can get so much worse. Perhaps I should value this moment so much more than I was prior to these thoughts.
Cormac took the very real, very disgusting parts of humanity and wove horrifying tapestries from it. But they're not purely for the sake of shock and disgust. The contrast of what he depicts — held up to most readers' realities — provides a heightened sense of the inverse of what he describes, allowing you to realize much better how beautiful the good parts of humanity are. Left to our own imaginations, most of us are not only unlikely to wade into that darkness, but we also lack the sheer depth and breath of skill he has in bringing it to life. What he offers is a sort of simulation of something otherwise inaccessible to most of us.
I'd make the case that without this exploration, our perception of life can be duller. I'd never want that dullness to be sharpened by real experience though; I'd much rather brush against that reality in the form of a story.
Human senses are calibrated by relative experience. Whether it be taste, sight, smell, touch, or even emotion: you won't recognize what feels good or what is better without experiencing what's worse in some way or another. The harrowing experience of imagining the vulnerability and suffering of loved ones or yourself might actually be an excellent tool for recalibrating and hardening your desire to see people safe and thriving. It may reestablish how crucial it is not to let the world descend into what Cormac describes. It can open your mind to possibilities you hadn't considered in ways that aren't strictly hypothetical or for the sake of pure masochism.