Good design is what engages your viewers. It can influence the psychological opinion of visitors as to what your company represents. It also has a positive influence on viewer retention. An attractive and effective designed website can lead to more pages being viewed which leads to more conversions of sales etc. To get your message across, you need for the visitor to be engaged and to be able to find information quick. If you site is not properly designed or has too many flashy items you may be discouraging visitors.