A fundamental principle of Agile, originating from its Lean roots. All teams know about the importance of limitng WIP but, as every ScrumMaster of FlowMaster will tell you - it's a very difficult goal to achieve.
It's simple to see who is trying to do too much, and is therefore not as effective as they could be. First choose the states across the board (1) which represent 'In Progress for this team.
The see who is doing what (2)
Clicking on the bubble (1) we can see exactly which items (2) Rory is working on.
Click (1) to show the items that have not yet been allocated to anyone but are within the release or Iteration