Structures the benefits of the mechanistic structure include clear lines of authority, a definite command-and-control structure for making decisions, and very clear role definitions. This organizational structure is excellent for business models where variability is costly and there needs to be a high degree of conformity of processes overall. The downside of this organizational structure is the lack of agility and flexibility, the tendency to limit employee's initiative and creativity, and lack of opportunity to rise on intelligence and creativity instead of seniority. Examples of companies with mechanistic organizational structures include process-goods manufacturing including steel, textile and chemical processing. In addition, armed forces are highly driven by mechanistic structures. Organic organizational structures have the advantages being very flexible and agile in response to opportunities and threats an organization faces, in addition to support for multi-directional communication and flexibility in job and role definition. There is also a much greater potential for employees...

The downside of the organic organization structure is the lack of clarity on roles, the lack of escalation paths for larger, more complex problems, and due to the shared role structure, a lack of accountability and transparency when an organization begins to lose focus. Start-ups including Twitter, Facebook, and Google are all structured initially as organic organizations as it enables much greater knowledge and information sharing.
References

Deborah Dougherty. (2001). Reimagining the differentiation and integration of work for sustained product innovation. Organization Science, 12(5), 612-631.

Robert Waldersee, Andrew Griffiths, & Jessica Lai. (2003). Predicting Organizational Change Success: Matching Organization Type, Change Type and Capabilities. Journal of Applied Management and Entrepreneurship, 8(1), 66-81.

Catherine L. Wang, & Pervaiz K. Ahmed. (2003). Structure and structural dimensions for knowledge-based organizations. Measuring Business Excellence, 7(1), 51-62.