Imagine you have a sheet with two columns: dates and values. You want to create a chart with this data, so you do. You intend to add to this data over time and would like the chart to automatically change with it, so you set the following for the Axis Title (=Data!A2:A) and the Value (=Data!B2:B)

The problem is that the chart's horizontal axis will not adapt to when the data ends. Instead it appears to default to 1000 rows. For time series data, this means that the chart will reach it's end, but only fill up a portion of the total chart size.