(Wa 3aleikum assalaam!)
I have a background in theatre production, so I am responding to this question thinking of the play as something that will be produced on the stage, not just read in a book...
Imagine walking into a theatre and looking at the stage set for a particular play. In simplistic terms, if the colors and lights are bright and cheerful, you might expect the mood of the play to be light and comedic; conversely, if they are darker and deeper, you'll probably expect something serious, dramatic or sad. (Note that many theatre artists like to challenge their audiences by contrasting the mood of the setting with what really happens in the plot...)
The time aspect of setting clearly gives certain clues to the characters' history, particularly if the readers/audience already know something about the time period, social relationships of the period, etc. For example, if a play is set in France in the 1940s, you can be pretty sure that World War II will probably have affected the characters somehow.
Finally, the exact place that the playwright chooses to set the scenes can give some history of the characters by, for example, showing their economic status (a wealthy living room, or a poor one), or where they spend their time (a bar, a kitchen, a forest, etc.).
This is by no means a comprehensive or 'expert' answer, but I hope it will help a bit!
yes it is expert, thanks so much, you are helpful.
