I just ran across this question in a LinkedIn group:
Do Typology Instruments Box People Into a Category Using Labeling?
My understanding is that Jung did not mean for his theories to be used as "labels." He meant them to help people grow and develop beyond a way of being. I have often heard people say things like, "I'm an INFP" or something similar. It makes me think people take these letters as a personality label and I am uncomfortable with that rigid interpretation.
Now, first of all, we should note that the phrasing used in the question is "I'm an INFP" or something similar. There's a big difference between a label given and a label accepted.
Personally, I'm not a fan of giving people labels (i.e. labeling; verb transitive). And, in fact, the ethical guidelines of administering the MBTI®, strongly recommend non-labeling language:
Present type preferences as tendencies, preferences, or inclinations, rather than absolutes. Though people have preferences and predispositions, all people have every capacity and function described in the theory of type.(They leave out the fact that all people do not have equal access to or comfort with every capacity and function.... But I digress.)
That said, it can become cumbersome to say "People with a preference for INFP tend to ..." every time. When everyone knows the language, it can often be a lot simpler to use shorthand wording, e.g. "INFP tend to ...". Even 'INFP' is itself a shorthand for "dominant introverted feeling and auxiliary extraverted intuition". This is why language shorthand (i.e. jargon) was invented.