Answer:
Business cards are great tools to introduce and promote a business. When someone visits your shop or office, you can give him/her a copy of your business card. You can also include your cards when sending bills and correspondence.
During events like trade shows, seminars and exhibits you can exchange business cards with fellow attendees or hand out copies to prospective clients. Business cards can also be inserted in presentation folders for future business associates to keep.
Source: http://www.digitalroom.com/business-cards-printing.html