This is mostly a Netscape issue, but it affects Internet Explorer to an extent as well. Table layout can really impact the user's perception of response time.
Netscape will not draw a table or its contents until it can lay out the entire table -- which means it has to have all of the text, all of the image sizes, et cetera.
So smart Web designers will break a page into multiple stacked tables whenever possible. That lets the upper table render while the lower table is still downloading.