Simply serious. Simple frames are generally best for serious work such as school reports and manuscripts, as well as for icons.
Drop in interest. Even a simple frame can add information to your text. In the image over the sidebar, the increasing percentages are emphasized by drop shadows that make the frames float above the page.
Lets Decorate. Fancy frames dress up simple fliers. They could also complement the copy, such as a border of sad dog faces on a Lost Dog flier.
Double-duty borders. In the ad for AccuScribe (see image in sidebar), the border for the ad also serves as clip art. Unusual shapes can draw attention to the frame contents especially when competing on a busy page, such as one full of advertisements in a newspaper.
Cut on the dotted line. Coupons in ads increase sales. Even when you arent offering a coupon, use the familiar dash line frame to give your ad the appearance of a coupon.