pre render event for rad grid

protected void rgStateTax_PreRender( object sender, EventArgs e )
{
if( rgStateTax.MasterTableView.IsItemInserted )
{
foreach( GridItem item in rgStateTax.Items )
{
item.Visible = false;
}
}

if( rgStateTax.EditItems.Count > 0 )
{
foreach( GridDataItem item in rgStateTax.Items )
{
if( item != rgStateTax.EditItems[0] )
{
item.Visible = false;
}
}
}
}

here rgStateTax is rad grid and,Why they are making item as invisible iam a beginner in asp.net,PreRender is the event before the page is actually displayed on the screen rite?.