Whereas row and column layouts only allow you to position a pane horizontally or vertically (depending on which class you use), grid layouts let you specify both, thus allowing you to create a complete grid of different CAPI panes.
grid-layout
supports a title column, as illustrated in
examples/capi/layouts/titles-in-grid.lisp
and it supports cells spanning multiple columns or rows, as illustrated in
examples/capi/layouts/extend.lisp
CAPI User Guide (Unix version) - 30 Aug 2011