[kumarvvr]

How is this different to, and better than using nested grids?

[psolidgold]

This is addressed in the article. This really shines when you have sibling dependent layouts.

[laszlokorte]

If you nest two grids, the rows and columns of two sibling grids are not forced two align.

With subgrid the rows and columns of two sibling grids are aligned with each other by glueing them to the rows and columns of the parent grid.