Background grids (Guides) are manual reference lines you align elements to by eye. Grid layouts are automated: you set the rules and your elements flow into place on their own, with support for mixed column/row sizes, responsive units, and real CSS output.
Use guides for fixed layouts (like print). Use grid layouts when you want automation, responsiveness, or code you can hand off.
For more information: Background grids vs grid layouts: what’s the difference?
