We looked at the relative success of our authors, comparing those that we know to have a plan with those that we do not know about. 

What we found was that those with a plan produced twice as much content as those that did not. However, what we also found was that having a SMART plan (Simple, Measurable, Achievable, Relevant, Timely) which is easy to understand is very important too. 

For most businesses, I think the idea that Excel spreadsheets are incapable of coping with the complexity of a content plan, would be a pretty good reason to simplify things. Or at least break the plan down into SMART components!