If I have a TWA, shoulder length or there abouts is as long as I'd have my hair. If my hair is longer, then I'd only go about 2-4 inches longer than my hair if we're talking braids or about as long as my own hair if we're talking weaves. I wear fake hair to get length necessary for style variation (so shoulder length instead of a TWA gives me more options). If my hair is longer, I wear fake hair to lessen the manipulation of my own hair and give myself a break from dealing with my own hair, which I do with extra TLC <--time consuming. And since I would hate it to be so obviously not mine, I'd not make it too much longer than mine.
I'd rather wear a weave shorter than my hair and shock people with how long my real hair is when I take it out, than show off this butt long fake hair and then appear bald when I take it off.