There are two primary limitations to CAD CAM restorations. (Like Cerec and E4D)It is not yet possible to do multiple unit bridges and the esthetics is limited. The esthetics has improved dramatically from the early days as the quality of materials has improved. Multi shade material blocks can duplicate dentin and enamel shades. Never the less, CAD CAM is not suited for highly esthetic situations. It is possible to create a CAD CAM veneer, cut it back and add baked porcelain to create a superior esthetic result. However this requires a skilled technician working in a traditional porcelain studio with lots of time.
The primary limitation for most dentists is the cost. A single system is well over $100,000. That is a huge investment for the typical dentist. However it is possible to justify the investment based on lab savings and time saved with no second appointment. For dentists who are already doing a lot of indirect posterior onlays and crowns it is a natural fit. But it could be a stretch for offices that still do a lot of amalgams.