This is a question more about projectors than Impress.
I am assisting someone who sends their presentation to members of their organisation for them to show it in village halls, conference centres, hotel conference rooms etc, where the exact projector available on the day is unknown.
What is the best format for their presentation when they don't know whether the projector and screen will be 16 x 9 or 4 x 3?
Should they create two copies of the presentation, one for 16 x 9 and the other for 4 x 3?
What happens if they project a 16 x 9 presentation using a 4 x 3 projector? Does it appear as a thin band (letter box) on the 4 x 3 screen? Or can they force the projector to show the full depth of the presentation while losing the Left and Right edges?