Never!
I had a colleague early in my career that owned airplanes. We used to fly together a lot and I will never forget what he used to say: You can never financially justify owning an airplane. You do it because you can afford it and you want it!
Abram
N301D
This is the right answer. I bought into a 4 way partnership early in my PPL training. I can afford it, so I did it. Here's why:
1) I'm a creature of habit. I wanted to learn in what I was going to fly my family in. I feel like I'm safer in something that I know like the back of my hand. The way the engine sounds, the avionics, where stuff is, etc... I did my first 5 hours in the school's Warriors - every one was different and it kinda drove me nuts.
2) Pride of ownership - nothing to say here, but state the obvious. Nothing like owning an airplane. I've owned boats, jet ski's, fancy sports cars, horses, and a whole lot of other cool stuff. Plane beats them all and it's not even close.
3) Convenience - We have a Google calendar that we use to schedule our plane. You take it when you want it. The group has never had someone 'hog' the plane and one of the guys flies so infrequently that whenever he does want to use it - we all gladly give it up...if there's even a conflict to begin with. There's nothing like being able to just show up at the airport, open the hangar doors, pre-flight your plane and go. No worries about calling ahead to schedule, worrying about the weather, unsure if the plane is going to be down for maintenance and you end up in something else, dealing with keeping the plane overnight or for any extended period of time, etc...
IMHO, unless you just have the $$ to do it, it just doesn't make ANY sense at all to own a plane outright. The obvious exception would be if you flew it all the time or had to fly at the drop of a hat and couldn't deal with anyone else having the plane. Otherwise, you have a fly a stupid amount of hours a year to even remotely justify the cost there.
One of the other really important considerations for me was to never be in a 'get there'itis' type situation. With my job as long as I have my laptop, an internet connection and a phone I can get stuff done. So, with my own plane I never have to worry about paying additional fees or putting someone else out if the weather turns and I can't get home. That was a huge deal to me.
I'll probably never do the actual math to figure out what I spend a year on the plane/flying but it's not cheap. Probably $1k a month or so when you factor in gas. Fixed expenses are a little over $100 for hangar/insurance and then we split everything else four ways. We put $12/hr into the TBO/engine fund so no one is writing $5-6k checks when the engine overhaul comes along (and partners can change too - so not fair for someone a few months in to have to pay for the TBO out of pocket when someone else burned up all the hours).
The obvious advantages to renting is that I could fly something I probably couldn't afford to buy or own - like a newish Cirrus for example or a G1000 something or other.
But, I just like being at 9500 feet with a destination - all the bells and whistles are great if you got them but it's not why I fly. So, that's why I own and probably the same reasons why most people who can afford to own on a budget do it as well.