How does the social-business letter format differ from the personal-business letter format?

1. How does the social-business letter format differ from the personal-business letter format? Describe three occasions that call for a written thank-you letter / What are form letters? What are the advantages of using them? 2) What are the disadvantages of form letters? Describe one way to offset each disadvantage / What are the ways in which companies can reduce the costs and time involved in writing letters?