The biggest reason for me considering a partnership in order or importance are:
1. I have not owned an aircraft before (besides a quicksilver ultralight I bought/rebuilt back in high school.) The ideal partner for me, would be someone that I can learn the ins and outs of aircraft ownership from. Honestly, I am a little concerned about jumping into ownership headfirst, and I think a partnership could be a good way get my feet wet.
2. It is very difficult to find hanger space around my area.
3. Although I could afford the aircraft, fixed costs, and operating costs on my own, it would be nice to be able to reduce those costs if possible. My wife and I have our first child on the way, and any large budget items are a negotiation. I could probably justify spending a little more up front on a nicer/better equipped aircraft if my costs where shared.
Additionally, I don't think the con's of a partnership are that big of a downside for me right now. I don't have a need to take the aircraft on short notice, so scheduling conflicts are less of an issue for me. My use case for the aircraft would be to fly enough hours to maintain currency and proficiency, and to make a few cross country trips per year to visit family or go on a vacation. I make my own work schedule, and can work from pretty much anywhere with an internet connection.