I think there is a point in having not more than one basic approach to life (Dominant function, that is), instead of some compromise between two or more. The Ti and Ni approach (for example) collide with each other and doesn't approve of the other.
It makes sense that one would be dominant, but the fact that they contradict each other is a good thing. For an ISTP, Ni will take Ti out of one narrow path of analysis, opening the ISTP to new ideas. For an INFJ, Ti will knock down Ni ideas that don't make sense. The functions have to keep each other in check because alone they're all pretty much useless.
Any good idea is going to be N (new idea to contemplate) analyzed by T (using deductive logic to see if it makes sense). S needs to ground N ideas in concrete terms, F needs to okay an idea to motivate T to analyze it.