It is commonly suggested that the most typical form of literary pseudonym is that of female oppression: female writers write under male (or gender neutral) names to get their books published.
All 3 Bronte sisters used pseudonyms with a stroke of amazing solidarity: they all took male names but used the same last name of Bell. The novelist George Eliot (of Middlemarch fame) was born Mary Anne Evans. But women aren't the only ones to choose a pen name for themselves when being published. Mark Twain (the great American author who wrote The Adventures of Tom Sawyer) was born Samuel Langhorne Clemens.
I personally think he should have been S. Langhorne just because it sounds cool.
And authors aren't the only ones to take pseudonyms. The majority of our celebrities do not use their real names or alter them slightly, for purposes of name recognition and branding. Actors, especially, must choose unique names, because their union, SAG, only allows 1 person of any name to be a member. In other words, if your name is Diane Keaton, you're out of luck.
In publishing today, pseudonyms are still a major factor. I know back in my MPW days, we discussed (usually in full-on daydreaming mode) what name we would write under. And did you know that JK Rowling is actually Jo Rowling, and the K is not part of her actual name at all? Rowling used the initials after her editor (or publisher, don't remember which) believed little boys wouldn't want to read something written by a woman. (Because Jo is so feminine, anyways.)
And the New York Times recently published a piece on the story of Patricia O'Brien, whose most recent novel, Harriet and Isabella, didn't do so well. After several rejections, including from her own publisher, O'Brien submitted the work under a pseudonym and the book was sold pretty much immediately. Whoops.
In this day and age, a name is branding. If you search just my first and last names, you'll find a whole bunch of people who aren't me - I have the most common last name in America after all. But if you search my full name, Drew Patrick Smith, then this website and my twitter account are on top. I have branded myself by making myself unique, so that my name holds some recogition value - at least to Google, anyways.
Pseudonyms can do the same thing - or they can help you to create a new branding if the old one isn't working out. The goal, though, is pick a name somebody else isn't using, no matter the field. You want your name to be the first thing that pops in Google.
Cause despite Beyonce's protests about girls, it's Google that runs the world.