"Healthy bodyfat level" depends first on what your body can support and second, on what your goals are. If you are a seasonal competitor, you probably need to maintain a lower avg bodyfat because its just as hard on your body to do massive weight swings repeatedly (I can attest to this...). It just gets harder & harder and I think later your body will enact its revenge. So keeping the on-season & off-season difference to around 15 lbs is probably a good approach. If you are NOT a seasonal competitor, then something that is "liveable" (i.e. fits your lifestyle & doesn't make you a constant bitch) shoudl be the goal. The biggest thing to understand is that the pix of competitors you see at show time is absolutely NOT what they look like year round, so dont' set goals like that. Just as you adjust your diet to achieve the cut phase, you should adjust to allow recovery, etc.
I think one of the bigger challenges in BB is AFTER achievign your goal, maintaining it or finding that maintenance point. If you rebound after you do hit your goal, then it seems like you spend the rest of your time trying to get back to that original goal, even though it may not be the appropriate goal anymore.