Advantage in few words

When we speak about outsourcing we usually mean that countries like the USA or Western Europe hire people or companies from the countries like India, Russia or Belarus.

India is a densely populated country so the labor cost in India is too cheap. Along with the cheap labor Indian software professionals are enough skilled and enough high mental level persons. This is the main reason that the US and Europe companies transfer their jobs in India. Also it's necessary to remember that English is a native language for most of Indian population.
In Russia or Belarus English is not native but most of people start learning it from the early ages. In Russia and Belarus the level of skills is also very high. And in many case European companies outsource to Russian or Belarus because they are closer.

By offshoring their jobs the companies will save a lot of money. According to a market research normally US and Europe companies save around 70% of their software development cost through offshore software development. In US the average salary of software developer is $9000 per year.