I you want to separate surfaces you have to click on every single polygon. Not very handy if you have complex objects with hundreds of them. It would be nice to have a "Live-Selection-Tool" wich selects all Polygons where I drive the mouse over it without clicking. (like in C4D)
Attachement: want to separate the WC
Well if you untick polygon and select the above option you will be able to select by angle ;)