Here are three good reasons that digital can make organisations much more effective:
b) You can also reduce duplication between the functions of the main business and communications. For instance integrated customer services and communications potentially allows your brand marketers to get daily customer insights at very low cost.
c) Measureability of digital is far better than conventional communications - so it's easy to rapidly understand what is and isn't working. This can be applied both at the strategic end of planning a campaign (e.g. testing alternative competitive spaces, testing messages) and at the execution end of the campaign (which media coverage actually drives sales?).
For a great example of a company that has put digital at the core of its entire corporate strategy, have a look at GiffGaff (a client of ours):
http://www.lithium.com/pdfs/casestudies/Lithium-giffgaff-Case-Study.pdf