Extreme obesity

A real FA would be at hand to carry his SSBBW around the house when she needs it.

You can't predict. My wife is not a feedee. She is average height and has never been close to 300 pounds. Recently, her knees and hip has given out and she is very immobile. Age has a lot to do with things. You may not have a problem being young and very fat, but add age to the equation, and you may become immobile.

All things being equal, studies show if you are obese, it's better to be pear shaped than to carry a lot of visceral fat.

Cartilage loss in the knees goes up even when you are overweight, and is near exponentially worse as you gain over 300 or more pounds.

Of course there are also the problems of cardio vascular issues, type 2 diabetes, certain cancers, higher risk of dementia in old age, hormonal problems and so on.

I am not trying to discourage you at all, just since you asked about the risks. I don't think anyone intentionally becomes obese for health benefits. It's like ultra running, no one goes out and runs 100 mile plus races because its good for them, they do it because they want to.