In my own opinion, giving too much weight to anyone's theory about "integrating an inferior" is liable to stunt emotional growth rather than inculcate it. I think it's best to take in information lightly and to listen primarily to one's own experience, letting the latter be more the guide.
Learning about personality types has been helpful to me in that, in listening to other NiFe'ers, I have gotten a better idea of what my authentic needs are. Many people show up here and proffer theory after theory about functions (sometimes it's their own theory, sometimes it's their interpretation of original text on theory- it's usually some amalgamation of the two, and quite often it seems like they don't realize how much they've added in their own interpretation)- but I personally haven't really gotten much from the generic formulations people apply to function theory; e.g. "focus on X task to strengthen Y function." The only time the 'inferior function' is a problem for me is when I am stressed- and ultimately self awareness (being aware of my needs and taking care of them) is what makes having Se as inferior less problematic for me. Reading other NiFe accounts and realizing sometimes my own experience is similar- cultivating self awareness from that- is how learning about 'cognitive functions' has been most helpful to my overall cognitive/emotional development.
tl;dr version: Yes, learning about cognitive functions has been helpful- but only when it's all taken with a grain of salt. eta: Ultimately I think Jung would say the purpose of all of it anyway is to help people integrate their unconsciousness/shadow- and I think knowing a little something about cognitive functions does help....but like anything else, if you learn it through rote instead of introspection (rote = memorize and regurgitate), it's likely to just add to the unconscious clutter instead of helping clean it up. That's my understanding, anyway.
I agree that integration of the inferior is highly individual thing and that there isnt some guide you can follow to gain the power of the inferior or something like that.. However there are some things that people can do and which depend on the type. For example mindfulness meditation for Ni doms is good, because it puts focus on Se purely. This sort of activation of Se due to meditation techniques can help Se to flourish more freely without dominant Ni getting on its way(which is the point in developing inferior), since mindfulness meditation basically is that, focus on sensations as they are and try to get rid of all thoughts, associations and feelings that the unconscious tries to evoke from the sensation.
But with other types it might be more tricky, especially those with J functions as dom/inferior. I havent looked much in other self-development techniques which could be helpful for other types, but mindfulness meditation seems like its made for INFJs. Then there is the battle of aux/tert as well, which imo at least in the case of INFJ needs to come from realizations in life. Like what i have seen in many INFJs is the Fe's need to be there for others, help them, support them etc. then one day realizing that it seems to be the only thing that people you have surrounded yourself with wants from you or they want it more from you than you can give, yet you give and give even tho it tires you, but maybe there is no one to give that to you. Or some variation of that. What this comes from is leaning on Fe too much instead of focusing on analyzing these people from logical point of view for example "If X only calls me when he needs a shoulder, then i am nothing much more than a shoulder to him. Being a shoulder for X makes me drained(= negative), i get nothing in return(=negative) and i am being treated as a shoulder only, even tho i am much more(=negative).". I know that the example is a bit black and white and i am sure that in clear cases like that, many INFJs even if they havent developed much TiSe will see as something not to do. But the thing is that real life is never that black and white, but its all shades. So what no book or technique can teach is where goes the line between acceptable and not acceptable in these shades of life.
I have also seen an INFJ irl go too deep into cynical mode because learning to lean on Ti too much because Fe "betrayed" her when she was only trying to be nice, but it just drained and gave nothing in return..
But the main thing in developing any functions is not just to train the function, but learning to consciously make decisions based on both thinking and feeling. The preference for in my case thinking doesent have to disappear, but the ego needs to learn to value feeling as well and what feeling says on stuff instead of just automatically 98% of the times choose thinking and not even hear what feeling says from all the thinking or ignoring what feeling says if its heard. What i strive to do with my T and F when they both have something to say(which ofc isnt always) is to stop and be like "okay thinking says this and that, then feeling says that" and from that start the evaluation of the situation and try to find a way that incorporates both or violates neither if possible. But to learn more trust in Fe in me and developing it to a level where it is at least somehow worthy of that trust is again something that is not as simple as stop and both think and feel..
