Perhaps the most interesting aspect of dissociative identity disorder is that it can be construed as a defense mechanism: that is, the mind is creating new people with different pasts in order to escape the horror of the past of the real person.
The reason why dissociative identity disorder is a better name than multiple personality disorder is that there is, in fact, a dominant, central personality. This person is a person, one person, whose mind has created an intricate means of escape from some insufferably traumatic past.
Among the alternative, dissociative identities of people suffering from this disorder are frequently children, i.e., people without much semblance of a past. Also frequent are extremely sensual alternative identities, which tend to act out the sexual urges of an individual who is frequently quite timid and reclusive, and often socially inept or unwilling. It is also not uncommon for there to be a "mischievious" identity, who does things that the dominant personality would never do, in order to get the dominant personality in trouble. When the dominant personality takes over again from the dissociation, he/she may find himself in bed next to someone he does not recall ever seeing before, or in some situation in which he must face the consequences of an action of which he would not have been capable.
There was an incident recorded in which an alternative personality was not diabetic, whereas the dominant personality was. This is possible, with this disorder: the brain is functioning in profoundly different ways for each personality.
The therapeutic treatment of this disorder is an attempt to combine and integrate these multiple personalities into the central personality, to make them aware of each other and in doing so to make of them a single functioning individual. This is done by making the dominant personality aware of things which have been done or said or drawn by a dissociative personality, and trying to make the dominant personality recall the closed-off memories accrued while acting as the alternatives. The individual experiences an amnesia specific to the times he is functioning as his "alters", and it is the overcoming of this amnesia that marks the first and most important stage in the "curing" of the disorder.
The paradox of this treatment, and the paradox of the diagnosis of the condition itself as a disorder, is that it is said to occur as a sort of defense mechanism against unbearable memories, against an unbearable past. The mind is creating these barriers--amnesia, "alternative personalities", escapes into mischief and sensuousness--in order to make the individual functional on some level, functional on an intimate level or a social level, and functional on a level that does not dread its own memory, and does not exist in a state that is perpetually haunted by things past. Dissociative identity disorder is in a sense a means of escape, a reversing of the irreversible, an attack on seemingly incontrovertible memory--and to cure it is to remove this safety barrier, so that this patient is returned to a world in which he or she can function, but at the cost of having to face the reality of the past.
Does the phenomenon warrant treatment? I'd presume that "dissociative identity" only becomes a "disorder" at that point at which the day-to-day functionality of the individual becomes impaired.
But then, I am far from an expert, and yield to more informed perspectives.
skepdic.com/mpd.hmtl