Why use a pseudonym when writing?

Rick Lowe

I'm often intrigued by people that use an assumed name.

Take Simon over at BahamaPundit.com for example. He's introduced as:

"Simon is a young Bahamian with things on his mind who wishes to remain anonymous. His column 'Front Porch' is published every Tuesday in the Nassau Guardian. He can be reached at frontporchguardian@gmail.com."

Usually very critical of people, writing stuff like this, he or she loves the FNM, yet refuses to identify him or herself.

How about Bahamas Uncensored, a blog said to be written by Fred Mitchell. Also very critical of people, but he or she loves the PLP, yet refuses to identify him or herself.

Many people write to the press under an assumed name as well.

Does a pseudonym diminish their message?

Does it make it more believable?

What's your take?