The theme allows for one-column and two-column layout. However, instead of having a select layout option in a theme options page, Reddle chooses the layout by adapting to the content of the user’s sidebar widget areas. If the widget areas are empty, then it shows a one-column layout. Otherwise, it shows the widget(s), hence a two-column layout.
That is a smart, logical idea that can be extended to more layout options. Want a three-column layout? Add the second sidebar to the available widget areas. If it is filled, automatically change to a three-column layout.
The idea here is to make use of WordPress’ built-in features and settings, whenever possible, instead of adding another theme option. I like that.