What I love about writing is being the master of your own universe. You get to take things you have experienced, people that you know, and change them or manipulate them however you want.
It makes me feel like going MWAHAHAHA! Or, sticking my pinky in the corner of my mouth, a la Dr. Evil.
At the same time, what I have discovered is that once I have my characters fully formed in my head, they start to retaliate.
For example, I am currently editing an urban fantasy that has some romantic elements to it. I tried to get my main characters to hook up, and they just wouldn't cooperate. Seriously. I put them together, and then the whole story would fall apart. So, I had to rewrite, and throw things away and completely alter story lines. It sucked. I really don't like not being in complete control of things, especially things that are going on in my own head.
Now, I finished the book, and the characters still aren't together. And more things are happening in my head, which means I am going to keep writing (a sequel!) and trying to get them together in between all of the torture I put them through.
And I'm still not completely in control. I swear to god, sometimes, I am writing and I look back over what I read and it's like something took hold of my body and wrote it for me. I think, "Did I really just write that?"
Super creepy. This is why writing makes me feel crazy. But, I think, it's a good kind of crazy.