Illustrate the benefits of Functional model

Functional model shows how values are computed. This model describes decisions or object structure without regard for sequencing.
It provides you dependency among various data and functions that relate them, giving flow of data.

Each process requires to be implemented as an operation in one or more objects.

Every data item arising from an object must have a corresponding attribute or set of attributes in source object. The data flow diagram (DFD) corresponds to actions in state diagrams of classes.

That is why it is suggested to construct functional model after both object and dynamic models.