Why should a company open source one of their products? and what is the business case?

If you where asked by a friend to help him make the business case to open source a product created by his company, how would you answer?

The scenario is a company that has a couple products and fells that it is not able to spend significant time and resources in one of them.

My answer was to 'just do it and push the support + maintenance efforts to the community'

Here are some links to good articles on Open Source business models:

• Business models for open-source software 
• Open source code and business models: More than just a license 
• Open-source economics 
• The emerging economic paradigm of Open Source 

The idea is to find the 4 to 5 business benefits this company, and to help him to make the business case to open source that product (which would be a great thing since the product is quite amazing).

Here are a couple 'Open Source related' blog posts that I have written before:

• Releasing a tool open source: how-to and what license? 
• Should the NHS IT Project go Open Source and what about its security? 
• OunceLabs releases my research tools under an Open Source license (it’s called O2 and is hosted at CodePlex 
• With O2, I am a Curator of Open Source Software 
• TraceGL (and the failure of the OpenSource commercial model) 
• Where Is .NET Headed? and the cost for Microsoft of ignoring the O2 Platform