You don't need to require classes that are directly under Ext (ext: Ext.Panel) but you do need to require them if they are in a deeper namespace. Ex: Ext.dataview.List
I must be missing something. I am using MessageBox and ActionSheet in my ST2 b3 code in my app and have not explicitly added any of them to requires. yet my app works fine. I'm just wondering if this will bite me later.