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Standard software
In the paragraph about software development it is already stated that development of custom software is always a bad alternative. Customers that are important for a proprietary vendor sometimes manage to integrate their custom solution into the standard. With open source this promotion is always possible. It is not dependent on your budget or vendor relation, but on the contribution of your solution to other users in the open source community.
Independence
Your contribution to open source software is an investment in independence.
No custom development
This way you can commit to the policy "no custom development" while fulfilling all business requirements and level ICT solutions to the max.