It is a matter of psychological 'style.' Being a control freak, I could never partner with someone in a biz. For my business model I found that it works better for me to pay people to do what I need done, leaving me free to handle what I really love doing: design and working with writers.
The key being this: if you love what you're doing, chances are you'll make a success of what you are doing. Many people I know function better in a 'partnering" situation, and I believe there are a lot of success stories in the porn biz that demonstrate this -- but for autonomous types, I think they're success is attributed to the challenge of doing things alone and benefiting from that position.
