I know that most companies outsource because of the cost-saving benefit which it brings to the companies. This reason was validated based on the results of the research done by Forrester.

According to the research, IT outsourcing could help companies save at least 10-20% a year. Conservative deals (selective outsourcing) could bring about 12% in cost-saving annually while a "sweet spot deal" (outsourcing deals which lasts longer) yields at least 17% cost-saving yearly.

The cost-saving which was shown in the research was a big percentage as compared to the actual cost-saving that companies experience. Maybe the companies which participated in the research had a step-by-step process in outsourcing - something which could be a big advantage in terms of reaping the advantages of outsourcing.