Karen,
I agree that there are some drawbacks of losing quickly. I do have gallstones now and if I eat something that is high in fat, the gallstones start moving out of the gallbladder and that is so painful. I haven't had any trouble since I've regulated how much fat I eat but I know others who have lost weight quickly have had worst complications with their gall bladder.
Also, if you lose quickly you will probably notice more loose skin than someone who hasn't. The loose skin will tighten up a bit over time but when you lose quickly, it doesn't have too much of a chance and it appears to be more noticeable.
The other reason I think of being cautious of losing quickly is weight loss and weight maintenance takes a lot of patience. If you lose quickly, get to your goal and then think, what do I strive for now? The scale isn't moving anymore but I still have to continue eating like this. How do I deal with my new body without gaining the weight back? I think it becomes largely a mental struggle at that point and some deal with it well while others may not.