Have you ever had trouble picking behind a transparent face in an assembly? Perhaps you are in the Edit Part mode and your system settings force assembly transparency for the components you aren't currently editing. In such cases you can see the edge or face you want to select through a transparant model, but SolidWorks won't let you select them, even though you may switch from shaded to hidden lines visible. Why?
The culprit is likely a switch in Tools, Options, DIsplay/Selection, Enable selection through transparency. If this switch is turned off, then as long as your model is transparent, you will not be able to pick trhough to hidden edges. Enable it, and you are able to pick through just fine.
You may very well want to leave that switch disabled, however, to lighten the system load or just make it less likely that you'll accidently pick through a model when you're working top-down style. In that case, to temporarily allow selection through transparency, hold down the Shift key and you'll be able to pick through the transparency.