IMO, the power that you need all depends on the extent of the area that you need or desire to light. Since light modifiers such as soft boxes and either shoot through or reflective type umbrellas provide the softest light when set up closest to the subject, massive power is not, IMO, needed for general portrait or product lighting.

This is doubly true if you are shooting in a rather small area such as the average house. Additionally, a softbox that works well for a powerful studio strobe is pretty large and unless you have a larger area in which to shoot, the large softbox is cumbersome...