To set limits
To provide a name or description
The child's eagerness and interest carry her over many obstacles that would be our undoing if we stopped to define and explain everything.
It will not be welfare (or, at least depending on how you define the term, it will not be perceived as welfare).
To discover and define those laws is the problem of history.
It is then possible to define by a parallel elaboration what is meant by classes of classes, classes of relations, relations between classes, and so on.