For me, a good theory is one that does one or more of the following:
- It allows one to predict what will happen, or
- It describes (explains) why something has happened, or finally
- It prescribes what one should do (this is a variation on 1 above).
In general, as a practitioner, it is the predictive power of a theory that makes it most useful.
I’m wary of theories that seek to prescribe actions (also known as being normative, as they say what is ‘normal’ course of action). This is because they are often not sensitive to the context in which action will take-place