Pros:

I get to create my own world. I am queen!
I reward myself with a chocolate break when I complete a chapter
I can do my work in my pajamas
I can eliminate a character if he/she gives me hell. If I only had that power during the holidays!
I get to help my heroine find the perfectly imperfect hero

Cons:

Every writer automatically becomes a critic (grimace); this means a badly written passage can jolt me out of the story line– very annoying
I have less time to read
Did I mention I have less time to read?
Marketing sucks!
It’s nerve wracking wondering how people will react to my story
When your main characters give you hell, you have to grin and bear it