it means you will never be able to ski again...
mounting them core center is best for the ski, also better for all mtn like the guy at ur shop said, and yes you can still use on jumps n rails it is just a little harder, for rails aim for the rain to be just about under or just infront of the front of ur binding, jumps are fine unless landing switch, then it gets a little harder but ud be fine
if ur that worried about how theyl hold up in the park then you should a park ski mounted center, but can also hold up for all mtn, such as the line chronics or somthin