Answer: To save money!

Well, that would only be part of the answer.

Freedom, sharing, a "better world", more education, more opportunities, .... all come to mind.

We should stress, that we have used the term "Open source" here without diving into the detailed analysis related or competing terms such as "free software" and the many licences discussions in the background. We want to focus on the changes and the benefits coming form the very wide range of freely and openly distributed software.

We are still in the early days of the internet and we are too far away from understanding the impact. Telephones and fax machines had been around for much longer before they really changed the (business) world. Telephone banking started some 80 years after the telephone entered our houses. Online banking followed within "months" - so to speak for comparison.

We are on the verge now to reduce the use of emails considerably. Social / business networking is taking over and with the change in communication and business processes hierarchies will flatten. And the changes in hierarchies will not be limited to companies. We do not have to filter inter-company communication any more by layers and people. We can do it electronically and the junior joining a company can be heard directly by the top dogs - online. If s/he has a good idea there is no reason why it cannot go straight to the top - or even better to where it belongs - the person who needs the answer to a tricky question.
Sure, there is the information flood and we will need to develop skills to deal with this. Google has shown that is where the money is - controlling and sorting information.

As the sorting of information is done in more and more clever ways, well may be just in changing ways in response to the changes driven by the online exchange, companies and society will have a much better "corporate" memory and less need to repeat costly mistakes. This will also reduce cost - let you save money.

Freedom of information will be key. Because if the information will be manipulated it will lead to mistakes. This is not new and the battle between those wanting to control information (knowledge) and those wanting to keep it free will go on and on. But only free information will allow us to develop new ideas and progress.

So, Opensource will be the main driver of the next phase in evolution - not just in the technical sphere.
And Opensource will also provide work for more people as it cuts out the middle wo/man taking unsustainable profits from basic software, services and processes. Opensource allows people to develop their ideas without large or even any investment.
Opensource puts the money and the profits where they should be - into producing real things.

There will always be special programmes required and commercial companies will produce them for profit. Opensource also provides profits for lots of companies, people, groups and communities providing their value added knowledge to build new applications. Opensource does not mean all is free - it just allows much wider access to basic tools and shares what may create "a better world" more fairly.

Opensource also puts people across the globe into contact and allows them to share their skills and abilities more efficiently. And Opensource makes the users independent of getting the service they need - there are hundreds, thousands, millions of developers out there who can help - not just a premium help line and single provider.