For coding it makes no sense to use any quantization worse than Q6_K, from my experience. More quantized models make more mistakes and if for text processing it still can be fine, for coding it's not.
The best image is the largest, takes up the most memory when loading, and while it is large and looks the best, it uses up much of your system resources.
On the other end of the spectrum there is a smaller much more compressed version of that same image. It loads quickly, uses less resources, but is lacking detail and clarity of the original image.
AI models are similar in that fashion, and the parent poster is suggesting you use the largest version of the AI model your system can support, even if it runs a little slower than you like.