Emotions: Useful, Distracting, or Necessary?

I am sure most of you writer-types out there are emotional. You have to be, to get the myriad emotions of myriad characters to sound remotely believable. I'm wondering if your emotions ever get in the way of your writing?

I'm put in mind of an often quoted theatre saying: "Emotions? I'm an actress - I have ALL OF THEM!"

I had a really crappy day yesterday, but I had time and inspiration to write. This is the first time these three things have happened at the same time. Usually when I write, I'm calm and pretty cheerful. I'm almost always pretty cheerful (calm, not so much), so this was different for me.

I noticed my emotional state before I started, actually tweeted about it, wondering how it would affect my output. I ws a little concerned, thinking that I was so wrapped up in my head that I couldn't get into my MC's shoes.

I was so wrong. The words flowed faster than I could type them...I actually ended up with a few scandalous and hilarious typos by the end of it. I wrote, not releasing the anger as much as using it. I didn't write about what was making me unhappy (my MC's life is nothing like mine) but I wrote about unhappiness, worry, anger, sadness, stress - all of it just came tumbling out far easier than I'd expected. It worked, that was where the story was going. I still wonder, however, how I would have fared had I been expected to write a happy scene of forgiveness and joy.

So I'm wondering, fellow writer-types: do you find your emotions to hamper you as you try to get lost in your character's voice? Or do you thrive in whatever mood you happen to be in when your fingers hit the keyboard?

Do you change what you were writing in accordance with your mood?