Depends on the model. Many of the cheap and light image generation models are trained to be good at the most obvious stuff so they can run on weaker hardware. They can generate perfectly realistic and consistent faces (and certain other body parts that are... in high demand) because that's what the human eye instinctively focuses on first, but will struggle to generate a wooden chair that isn't a weird M.C. Escher mess. You can run those models on a consumer GPU to generate multiple images per minute.

Not all models are trained with those limitations. Some can get scary accurate and consistent.