Main purpose - is total bandwidth calculation and calculation amount of packets coming through device in second.
As I see, the only way do it now - using stackable graphs. But this way has a lots of inconveniences, such as:

• the 'legend' of the graph becomes huge when adding a lot of ports (eg on a 24port or 48port switch)
• the graph becomes slow to render
• the graph shows artifacts (when some ports are not used, the lines of '0' height are darker than the rest of the filled graph)
• adding 24/48 items to a graph is a lot of work (even when done directly in XML files).
  The right way to solve such task: create 1 item to collect data from some other items, then (if needed) create a graph from the 1 collecting item.