Multiple Layouts

I have already read the best practices and performance portion on the manual.

Is it better to create a new layout for each level for a game like Tetris, where each level is almost identical.

For a game like Zelda, should I create a new layout for each section that the character goes to? Or should I just create one massive layout for all the areas? What is better?

Are all layouts loaded at the beginning or are they loaded based on an event?

Thanks