What does speaking in third person denote? Is speaking (or preferring to speak, even if not actually doing it) about oneself in third person a symptom of any specific mental condition?

I can remember a person in an IRC role playing chat room who preferred to speak this way. But apart from this specific case, I am also asking in a broader context.
Speaking about oneself in the third person is known as illeism.

It is not a symptom of any mental condition listed in the DSM. As Wikipedia notes, it is sometimes used in speech and literature for stylistic reasons.