When asked what period or time she is setting a new play in, Mary Zimmerman replies "the Gorgeous Period."
Does this work for every single script? Of course not, but the theory behind it does.
Rather than confining a production to the clothing, architecture, technology, customs, etc. the director is allowing herself the freedom to pick and choose the elements of the play to suit the scripts needs. This allows the actors and designers a unique advantage in telling their story; rather than trying to assign meaning to an object or gesture, they can use the object, gesture, or whatever that means exactly what they need it to mean.
Zimmerman takes it one step further. She also wants every single item that appears on stage to have a sense of beauty. This shaping of her aesthetic gives her productions an identifiable feel that is original and her own.
There are, of course, many plays that require the exact opposite aesthetic of gorgeous. Desolation and ruin can be very effective stage pictures and conjure very strong reactions. But the rules of the "Gorgeous Period" can still apply in the specific choices that are being made.
The whole point is to create a world within the theatre that you can manipulate effectively to tell your story. Nothing appears on stage by accident. If the director, designers, and actors pay careful attention to what they choose to include in their story, the audience can be easily drawn into this world. If you don't know why something is on stage or can't justify why you are doing something, you should probably do one of two things. One: figure out an answer to the why. Two: remove or change the element.
The second option can turn into a slippery slope. Removing something just because you don't understand it is never acceptable. If the playwright has included something, the general rule of thumb should be that it is not only important but essential. However, if you are adding something just to add it or make a statement and you find you can't justify it - that is when it should probably be removed.
But be deliberate in your choice. The audience will accept anything as long as it is well thought out and given a context of support. The will, however, immediately see through something that is not fully part of the world and become frustrated.
Don't frustrate your audience, welcome them. Invite them to join in the story. Give them something gorgeous to take with them as they leave the theatre.