That assumes that what the individual is attempting to do is a) self promote or b) play someone MORE interesting than themselves.
Rather than simply someone other than the day-to-day self that they feel should be rather more private/protected. And actually, that's not that hard at all. (Trust me.)
The purpose, rather, or at least my purpose when I do the same thing, would be to separate my actual self (the one who gets crabby when she doesn't have enough to eat and has days where she can't adequately access language, etc) from the person with whom everyone else interacts. And I do it all the time. My voice students don't get to interact with M the person (for the most part), they get to interact with the deliberate construct of M the voice teacher.