A worsted windowpane, of course, is less formal than a pinstripe or solid of the same color and fabric. And in my humble opinion should be worn on those occasions you do not want to present a "power" look but want to appear more approachable. I wear mine for business when I'm seeing people with whom I already have a friendly relationship. The particular fabric also should be considered. A navy worsted with a subtle window pane is more formal than a solid tweed. And as an exception to the general rule, in my opinion ,a tweed windowpane is sharper than a solid of the same fabric.