Glossary
CFG Scale
Short answer
The setting controlling how closely the model adheres to the prompt.
At a low CFG the model reads the prompt loosely, giving more creative results further from your brief. At a high value it binds tightly to the prompt but the image starts to look saturated, harsh and artificial.
For most models the 6 to 9 range is balanced. Values above 12 usually degrade the image.
A high CFG does nothing with a short prompt — there is not enough information to bind to. With long, detailed prompts a higher value can make sense.