Different screen layouts are useful for different scenarios. If you are a laptop user developing tests, running tests, and analyzing results, you will probably prefer your laptop's native screen resolution, which may be fairly high. In general the higher the resolution, the more panes you can view at one time. For such scenarios it makes sense to use High Resolution screen layout, which enables all panes.
When viewing Silk Performer on a low-resolution device or during the course of a presentation over a projector or Web meeting, your screen resolution will likely be more limited. For such scenarios it may be useful to use normal screen layout.
The customizations you make regarding the panes that you enable/disable and the positions in which you place the panes are saved along with both your high resolution and your normal layouts. For example, if you reposition the Project pane while working in high resolution layout and then switch to normal layout, the Project pane will appear in the same custom position the next time you return to high resolution layout.