Most plays are presented as if they take place in several different physical settings and over a span of time longer than that which the audience has actually been sitting in their seats. The last line of Act I, scene 3 is said, and the first line of Act I, scene 4 is spoken by a different person, in the following Summer, in a different part of the forest.
The solution too many Directors reach for to cover while the actors change places, the furniture is moved, set pieces are shifted, etc., is to turn off the lights and then turn them back on when everything is ready.
I would swear that some Directors actually believe this is like making a cut in a film. The lights go out, then come back on and magically we are somewhere else.
Reality is that there is no such thing as a blank, a void. You don't present "nothing" by turning out the lights. You present something different. Usually (and especially in the smaller, less professionally-experienced theaters) what you get is several long minutes of shadowy figures visibly fumbling around in the blackness, cursing quietly as they try to find their spike marks.
John Cage's point was that the "silence" of a concert hall was filled with the sounds of rustling paper, air conditioning, coughing, shuffling feet. And to him this was on equal musical footing with a piano concerto. Perhaps. What is certain is that the activity of scene change has a specific character -- and it may not be in keeping with the character of the play.
The more charitable interpretation of what is expected to take place in the minds of the audience during a theatrical blackout is that it is akin to a commercial on radio or television. The audience skips over it, edits it out of the experience of the play in the same way they don't include intermission as part of the world of the play.
I still find it distracting. Watching a scene change, especially a difficult scene change, takes me out of the play. Intermission only happens once, and it happens at a dramatic point that practically demands you sit back and take stock of the situation before heading back into the action. Scene changes break the flow. A slightly better argument is that scene changes, like the velvet seats and the proscenium arch and so forth are part of the total experience of live theater. One watches certain shows (Phantom comes to mind) for the moments of "How did they do that?"
But other shows -- many, many shows -- the Directorial intent is to distract as little as possible. To keep the audience immersed in the story and the world of the play. And I have to say to these Directors -- I have said, and more than once -- that a blackout fails to accomplish this.
Because especially when you've got an awkward set and less-skilled crew people, the actual experience of a blackout is the discomfort of watching dimly-lit people struggling.
Better, in my opinion, to light it. Put enough light on it -- I like the term "Change Blues" because Directors get what I'm after almost immediately -- so the crew can find their spikes and move with grace and surety instead of fumbling and trying to hide their flashlights. And take the time to work out the changes, to choreograph them a little.
And, depending on the show and the design, you may be able to do the change au vis. When we did Shrek not long ago we pushed the rolling units out in full lights. And more than that; I made sounds for them so a tower would grind on with a sound of stone against stone, and Shrek's house would pop up like a mushroom sprouting with squelching leafy noises.
This is, for some shows, going too far in the other direction. And I have no problem with a blackout if you can make the necessary changes in under thirty seconds and without a lot of noise. But otherwise: it is my strong opinion that you are going to see it anyway, so instead of pretending you are hiding it and achieving nothing but hazard for the crew, discomfort for the audience, and a less-than-stunning visual image, you should light it enough to make it pretty. And make the whole thing go faster and smoother so you can get on with the play.