We probably won't do it, but it was more of a curiosity question.
JP Sousa spoke toward your question very well, but I'll chime in to say that it's really a convenience and a safety issue.
If you have a generator that is portable and you don't connect it to your household system via transfer switch, you're going to have extension cords running all over the house, you're going to have to feed that gasoline-powered, noisy generator gasoline at all hours of the day and night, and it's just generally safer with a permanent setup -- not to mention a real plus when you're trying to sell your house.
Maintenance of a standalone generator consists of changing the oil, oil and air filters, and if you've got a Generac, adjusting the valve lash on occasion.
(My Kohler requires no valve adjustments, TYVM.) So maintenance is pretty straightforward and easy. Engines are sturdier and better able to handle loads, and it basically boils down to "you get what you pay for."
YMMV.