Most of the point are covered in the discussion above but I would like to add some more points to it.
Cost And Efficiency Savings.
Reduced Overhead.
Operational Control.
Staffing Flexibility.
Continuity & Risk Management.
Develop Internal Staff.

Disadvantages:
Possible loss of control over a company’s business processes
Problems related to quality and turnaround time
Sluggish response times coupled with slow issue resolutions
Shortcomings in performance vis-a-vis expectations
Lower than expected realization of benefits and results
Issues pertaining to lingual accent variation
An irate customer base coupled with enraged employee unions