I.e. if you want to store something on an executor but you don't want to disturb what's currently going on at the stage. Then (with an empty programmer) you press the Blind key, select some fixture, do what you want to do, store it, clear the content in your programmer and then press the Blind again. Nothing happened on stage, it was all hidden from the output.
If you deactivate blind while you have values in your programmer, then these values will become visible on the output. If you have an active Program Time fader, then it will use the time set on the fader - read more about the Program time fader in What is the Programmer. or in the Magic Speed view.
Similar, if you activate blind with values in your programmer, then these values will be hidden from the output - changing the current look on stage.