I feel that filtering “On selected element and its children” is the best mode of Problems view filter, because it allows you to very quickly narrow down the scope of reported problems: click on Working Set (in Package Explorer), and it shows all problems in all projects in the set; click on a project – and only problems in the selected project appear. Click on individual class (or package) – only problems in the selected class (or package) are shown. So you don’t get distracted with problems unrelated to your task at hand.