I always liked to view Technicals as having their original potential "inverted" or "altered." Like Ichor says, No one really knows the definition of purpose of the Technical Form. As I see it, the Technical Forms always have abilities/roles which differ from their original form.
Not too many of them are very good either. Though some are good, some are doomed to be jacks of all trades - masters of none. For example, no one seems to know the niche of Technical Cirno.