A scenario is a group of component placement commands and signal assignment commands within a layout database. A number of different scenarios can be created, and you can switch between them to explore different variants. Each scenario is independent and does not take effect to the design until it is applied.
Scenarios allow the exploration of different layout solutions which may consist of different component orientations (e.g. connector located on the left or right side of the device) and different applications of unraveling. The I/O assignment can be optimized based on different component orientations and have the best solution propagated to the PCB layout process.
The first entry in the Layout Scenario window is the initial scenario - the initial layout of the design as it has been imported. When changes are made to component placement or signal assignment in a layout database, a new scenario is created, and will appear in the Layout Scenarios window. A green arrow next to the scenario name indicates the currently active scenario.