For image generation it does. They give negative prompts like "wonky", "creepy", and "ugly", and the image generator evaluates how well the generated image matches those prompts, and produces images opposite those parameters.

Some poor artist in the training data not only had their work stolen to train the AI, but also had it labeled ugly and wonky.

It won't affect the output meaningfully except by rerolling whatever training data ends up being associated with that or whatever. It may end up getting the model to "check" its work which just compares previous output to training data.

Earlier LLMs it helped a bit.

Now a days the harnesses know to spawn 'review' agents which will catch some mistakes but not all.