When doing XAML with Blend 4 in the designer each control has a little eye toggle. This let's you hide parts of the interface while you work.

 

Visibility can also be controlled per control with the Visibility="COLLAPSED" tags. It would be extremely useful if there were two eyeballs in the control list. The left eye would hide controls in the xaml in the designer. The right eye-ball would show hidden controls in the designer.

 

That's not confusing right? The object list shows - | hide control in designer | show hidden control | lock control | - and then each object has a visibility control.

 

Sometimes you want to toggle control properties without making changes to the XAML.