Yes, the weight limits are there becuz the machine won't work properly for you; and you may get hurt as CANDO says. At first, on my treadmill, the tread wouldn't move smoothly; later when I lost lots of weight, it started moving so fast that I fell. That scared me so bad that I haven't been on it since. We tried slowing it down, but it has a bottom speed and I walk like a snail becuz of injuries: I fractured one leg and dislocated the other knee.
So I am limited on what types of machines I can use; so I just went back to plain old-fashioned WALKING and SKI-WALKING for winter (regular walking with ski-poles for my arms which gives a whole body workout). Later on, I added my rowing machine, which I just use the arm motions and will add legs later. I still think your body has the best built-in exercise: WALKING. You can do speed-walking or sprint-walking if you need more resistance.
ROSEBUD