In battery-powered devices, a power switch can help provide extra safety, as well as isolate parts of a circuit or sub-systems from the battery supply when not in use. This can significantly extend the lifetime of a battery cell, which is how some products today can achieve many years of operation from a single cell.
As a load switch, a conventional electromechanical relay is not very flexible. Similarly, as a safety device, a fuse is not versatile. A solid-state power switch provides a much more versatile, flexible, and useful solution. They are small enough to be integrated into any electronic product, even wearables, and IoT.