The PanMode property is useful in scenarios when you want want to have a fixed zoom and allow the user only to scroll. This can be achieved by setting ChartPanAndZoomBehavior.ZoomMode to None and setting RadCartesianChart.Zoom to e.g. "2,1" -> chart will show the full Y axis range and only 1/2 of the X axis range.
On the other hand, if you want to leave the ability to zoom-in and zoom-out to the user, you can leave PanMode to None and set ZoomMode to Horizontal, Vertical or Both, depending on your scenario.
If you have any other questions, I'll be glad to help.
the Telerik team