I use it when I study science and generally when creating anything with structure such as lesson plans, essay plans any kind of design really...
It's also the function I use to rip a part the logic of people with Fi or Fe who are getting on my nerves. I know that I come across as a totally ruthless, unfeeling bitch... but some people deserve that kind of treatment... I guess that's my Ti speaking now lol
In our society T rather than F arguments tend to be more respected so I have found it useful to develop Ti.
Tertiary: Introverted Thinking (Ti)
The downside of Fe, of course, is that it depends exclusively on the judgments of
others in its ongoing effort to be judged as a morally sound example of the best values its communities (friends, family, coworkers, any groups to which the INFJ feels emotionally connected and responsible for) hold dearly. One may wonder, then, where the INFJ's sense of personal principles originates, if Ni simply perceives as many conceptual possibilities as it can, while Fe derives its evaluative principles from the moral fabric of its external surroundings.
Enter tertiary Ti: When all else fails and no meaningful conclusion can be reached via the Ni-Fe approach, the INFJ will turn inward again and listen to whatever his conscience tells him is inherently consistent, fair, and reasonable. The value in Ti's approach here is that it provides a sense of definite and complete closure to an INFJ in the middle of a conflict over which set of external moral values should be granted highest priority. Return to the basic axioms of what we do know for sure: "I think, therefore I am." When externally derived moral values have become too convoluted or too compromised to be trusted with a personal decision, Ti steps in to provide a personalized logical framework which can be universally applied regardless of context.
It gives us something we
can know for sure because it seems inherently correct and consistent in and of itself, and that can be quite a relief in times of internal strife. When an INFJ gets overloaded with too many possible interpretations of a problem, and can't find any useful objective guidance, he turns to Ti to decide what's ultimately reasonable and important to
him. From this he can derive personal convictions and find a way to make private value judgments without feeling he is neglecting the vital opinions of his community or locking himself into a limited interpretation.
Ti can have a negative impact when it's poorly developed or when it blocks out Fe to an unhealthy degree--the NiTi loop INFJ is brutally anti-social and absolutely clueless as to how to relate to the rest of humanity. One INFJ friend describes Ni as, "a very deep hole that it's very easy to get lost in and never come back."
NiTi loop can have even worse implications: If Fe is weak or underdeveloped enough, the INFJ may display so few outward signs of emotion that he is seen as uncaring, unsympathetic, selfish, and pretentious. Ti suggests a framework of logic for dealing with a problem, but there's no source of objective data to stop Ni from noting all the inherent assumptions in Ti's approach and short circuiting the INFJ's confidence in his entire cognitive process.
In the end, Ti serves a useful and much-needed assistant to Fe in the judgment process, but it will
not function on its own as an adequate substitute for objective, externalized Feeling judgment.