Apart from the semantic issues that result when littering your HTML with <table> tags that inaccurately represent the content they contain, Grid also provides features that tables cannot do:

  * overlapping cells (http://gridbyexample.com/examples/example15/)
  * empty cells, without a bunch of empty <td> tags (http://gridbyexample.com/examples/example12/)
  * size columns (or rows!) in proportion to one another
  * complex alignment of contents within a cell (http://gridbyexample.com/examples/example24/ and http://gridbyexample.com/examples/example25/)
  * specify exact min and max sizes for columns & rows
  * provide a full definition of responsive behavior, often without any media queries

It also provides everything a table does with far less code and easier to read markup.