However, when they do:
If Te>Fi (the case of TJs), then Fi will act as a moral filter for the decisions that Te makes.
If Fi>Te (the case of FPs), then Te will act as a rational filter for the decisions that Fi makes.
What Chazz said is correct. Two judging function working in tandem constantly will create internal tensions and imbalance. However, when they do:
If Te>Fi (the case of TJs), then Fi will act as a moral filter for the decisions that Te makes.
If Fi>Te (the case of FPs), then Te will act as a rational filter for the decisions that Fi makes.
Think of it as looking through the ocular device from National Treasure. The incoming light will give a different image depending on the filters you use.
When a function is lesser in dominance, you will notice a strong tug when it's active. It has its presence. You can see that when TJs have strong sentimental streaks or when FPs can have rational and orderly actions taken, which both can be out of character for each. (I am stereotyping here to clarify the concept).
F types commonly confused for T types:
ENFP (Ne>Fi>Te>Si)
ESFP (Se>Fi>Te>Ni)
T types commonly confused for F types:
INTJ (Ni>Te>Fi>Se)
ISTJ (Si>Te>Fi>Ne)
For me, I believe the Te-Fi combination is responsible for organizing and prioritizing which extends to feelings and values too.
Fi:
"As a cognitive process, it often serves as a filter for information that matches what is valued, wanted, or worth believing in. There can be a continual weighing of the situational worth or importance of everything and a patient balancing of the core issues of peace and conflict in life
I tend to think that Te and Fi can work rather well in harmony. Te basically plots the most efficient way of making something happen and Fi gives you the inherent value that Te uses to decide what is the most efficient/least cost effective manner of doing something. That's how I think it works in me anyway
I like to think Te and Fi work in tandem for me.
Seems like when I feel something is worthy of my concern, I have the capability to plan out what the best way to carry it out would be.
Fi=values
Ne=possibilities; schemata
and Te makes the plan and sets it in motion
Values are refined through Ne (by objectively looking over options/seeing if my values align with reality) and then made into plans or strategies or carried out with Te.
Without properly developed Ne, an INFP is prone to being judgmental, prejudiced, and reality avoidant (As Morgain mentioned.)
Fi and Te cannot work together effectively without properly developed Ne--the go between guy!