Symmastia is extremely sexy because it makes them look more unnatural. It's a shame there's only been 1 girl in pro porn with major symmastia (Allaura Sweet).
it's physically painful most of the time, and it tends to get worse, thus it's psychologically destroying. it's also a complication that once you've had it, it's very difficult to have repaired properly and can come back. it can destroy dreams of going bigger as well, because it tends to get worse the bigger the implants are. some surgeons are good at repairing it, but they are few. and it gets expensive. it's nothing positive, really.