I've talked about this before. I write characters and situations that are real, at least to me. The people in my stories are the people around me. If something weird happens in a story, it's something that at least in some small microscopic way has happened to me (or someone I know).
That's not saying that every story I write is an autobiography. It's not. It's a created 'skewed' reality. If there's a serial killer in a story, it's someone who's pissed me off in my real life. The bright and shining hero.... that's the hubbs. The damsel that's usually in distress (and yet happens to figure everything out), yeah, that's me. Any cast of helpful or not so helpful side characters.... pretty much anyone else in my life that has a personality that matches what I want to portray. Cheating? Maybe. But I'd like to think that it's more of an homage, rather than 'making fun'.
But it's a way for me to make sure that my story is as realistic as I can get it. I'm not the type of writer that fills her stories with unicorns and fairies. Not that they aren't cool as hell, I just don't want to create a whole new universe from scratch. I'll let other people do that for me.