[jjbickerstaffe]

Energy harvesting is useful where the power need is very low and changing batteries is inconvenient and/or expensive. So it makes sense where you need to deploy a large network of low power sensors. But ordinary batteries or mains power should be the default choice for most applications.

[BrandoElFollito]

Smart wall light switches are another place where they are beneficial (in places where you do not have the neutral)