For example, in bootstrap or some other older layout framework every "column" would need to contain some class or id to style it correctly. So for a 3 column grid you would need to give each element a class setup of something like "column-third".
With grid, all that layout logic is moved into a single container "display: grid" element, making it so much easier to add/remove/edit grid items. Even padding is declared in the container element with the "grid-gap" property! It's a small improvement that has immensely increased my developer experience building grid-like UI.