There are numerous theories of personality--each with their purported degree of accuracy and precision--based upon anecdotes, empiricism, conjecture, or a mix of these factors. Some have become a mainstay in actual psychological pedagogy, nominally the Big 5, while others remain fringe science. All of them have one common goal: to succinctly and adequately determine facets of personality that are measurable and predictable within the theory's paradigm.
Yet what does the individual gain from these metrics? In the Big 5, traits are seen to be relatively stable and largely immutable; thus, "knowing" the degree of which traits you or another displays will only serve as a marker of sorts, giving you or others an idea of what to expect. For the individual, they existed as they are prior to the tests' administration and will likely, according to the Big 5, continue to function in much the same fashion. Now, however, enters in the chance for peigenholing.
From my short time here, I've witnessed certain individuals (who shall remain nameless as the shitstorm abound here seems not to need any furtherance) embody their types to a degree that seems almost satirical. What's "worse" is that they expect certain behaviors from duals/conflictors, which seems to overly influence their perception of an individual. Having little if any standardization in terms of typing the process, people are far more likely to be mistyped, yet there is little if any conception of what constitutes a mistyping because of said ad-hoc typing process.
This, however, is not a shot at socionics or the Big 5; I have used these as only examples. I believe most psychological metrics to be self-limiting and moot, unless used to determine some underlying pathology. But in the absence of presumed pathology, which can only be assessed by licensed professionals, is there really a need for any of these delineations?
Before someone asks the nearly inevitable, "then why are you here;" I find these theories viscerally interesting yet throw a mental blockade up to prevent me from applying it, if at all.