I see my posted type code is a shorthand, a way of saying that, for the most part, I have the preferences, tendencies, and outlook of this type. Absent type codes, I might include some of these details as caveats in various messages, to help the reader better understand the perspective I am trying to describe. Eventually people will get a sense of my personality just from how I write, but new or irregular members won't have that yet.
On the flip side, I am not very good at relating others' type codes to who they are and how they express themselves, especially online. I use them mainly to cross-check when the discussion becomes type focused. In other words, if someone is posting about how Ti-doms operate, I might check to see if they are one.