In PowerPoint, the entire chart data that shows up in the form of series and categories is actually stored within an Excel sheet. These series and categories may show up on your chart in different ways depending upon the chart type. Almost any chart type, even if it is not a column chart, compares one set of values with another. 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 them as and when you want to expose those values.