A hammer drill provides large axial forces (in the direction of drilling) to material - i.e. Hamming the concrete while drilling makes it more effective. An impact drill provides large rotational forces to overcome friction of drilling. An impact drill can easily put a 4" screw into wood with an impact drill vs. a traditional screw gun where you have to push harder as the screw deepens. Note, both of these are very loud and should not be done during normal business operations if possible.