Postcards can be printed 1 or 2-sided and are often used as a mailer. This is mainly because unaddressed admail is cheapest than traditional mail and post cards do not require envelopes. Club promoters also use post cards often to promote special events or nights at a club. There are sizes and die cutting is also a commonly done to enhance the effectiveness of these marketing pieces. Rounded corners are also a popular option. This is also used frequently as a counter top or tradeshow promotion tool.