I don't think anyone in the world can claim that they use 100% of Microsoft Office suite's functionalities, including its designers and implementers.  Not only are people not using all the features, they are either not aware of or don't know how to access the unused features.

I personally use only around 10% to 20% of Word and Outlook functionalities, two Office apps I use daily.  I use PowerPoint about once a week and use 40% of its functionalites.  I almost never use Excel nor Access.  Visio, I use whenever I use PowerPoint.  Just eyeballing the numbers, I would say that about 80% of the Office suite is not being used.  That is waste of money.

Similar claims can be made against Microsoft Windows although the figure would be higher for me since I am a software developer and I know its ins and outs.  All the features and UI to access them are hidden beyond nooks and crannies that most users will never get to nor remember how to get back to.  Its like wearing a jacket with ten thousand pockets.

[a picture of Flint holding Tasselhoff's bag of holding]