No no, I don't mean them installing their own systems vs Solar City doing it.
If you have a PPA, the installer reaps all of the financial benefits. If you finance the system, you get all of the financial benefits. Its the difference between leasing a car versus financing it and then driving it until the wheels fall off (keep in mind, panels have a 25 year warranty but will still produce above 80% capacity for decades after that).
You could say that for pretty much every service you buy. Yet people keep spending money for things they could do (cheaper) themselves!