PowerFX allows to make some quick small logic changes and can partially substitute:

Business Rules

Power Fx formulas can be an alternative to business rules for simple calculations, field visibility conditions, or field requirement logic. Power Fx provides a more flexible and expressive way to define such rules than the limited options available in business rules.

Workflows

Power Fx formulas and Power Automate can handle complete workflow scenarios. Power Automate provides more advanced automation capabilities, integration options, and support for external services. At the same time, Power Fx formulas can be used within Power Automate to define formula-based conditions, data transformations, and actions.

Small plugins

While Power Fx may not fully replace the capabilities of plugins, it can handle many simple business logic scenarios. Power Fx formulas can automate calculations, update fields, or trigger actions based on specific conditions, reducing the need for custom plugins in some instances.

Primitive JS scripts

That can help people without development experience add some features to forms. However, it is essential to understand that it cannot replace JS or C# code due to its limitations.