Use your own judgment regarding whether you need to apply any cheats or manipulations to your shadows. With computers getting faster and production schedules always placing demands on your own time, it might not always be worthwhile to spend extra time setting up a fake shadow just to speed up a rendering.
On the other hand, learning to think on your feet and cheat or manipulate any aspect of your rendering is a valuable skill. You are always better off knowing ten ways to achieve something rather than being boxed in to a single solution.
Some cheats and tricks are useful not just for saving rendering time, but for giving you more convenient and direct control over your output, which enables you to create the most appropriate shadow qualities for your scene.