In PowerPoint 2011, the entire data that shows up on your chart in the form of series and categories is stored within an Excel sheet. These series and categories may show up on your chart in different ways — sometimes as an individual column or a set of columns within a column chart. For some charts, this data may also be represented as values or a legend. However, almost any chart type — even if it is not a column chart compares a set of values. Once you delete any of these values, they no longer show on your chart — so the level of comparison reduces. However deleting is not always the best option, especially if you want to retrieve those values later whenever required. The solution is to temporarily hide values you no longer need — and then unhide as and when you want to expose those values.