The spindle is firmly attached to the bearings on the drill. This produces great precision concentricity. The metal drilling speed is optimised. With an impact drill, the spindle is positioned amongst the bearings such that it can move freely. Depending on the system, the precision concentricity is not as good as with simple drills. The speed is generally higher than that of simple drills, because impact drills are also used for drilling stone, for which you need a high impact rate.