In Visual Design, what does this mean. Are there examples?

What is meant by this?

Use an 8px-by-8px grid. A grid keeps lines sharp and ensures that content is as crisp as possible at all sizes, requiring less retouching and sharpening. Snap the image boundaries to the grid to minimize half pixels and blurry details that can occur when scaling down.

In Visual Design, what does this mean. Are there examples?
 
 
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