We consider a lower weight better because lighter devices are more comfortable to carry. A lower weight is also an advantage for home appliances, as it makes transportation easier, and for many other types of products.
Higher speeds work better for drilling holes in certain types of material, such as steel, aluminium, concrete, etc. The drill speed is measured in rotations per minute (rpm) when the drill has no-load.
An impact drill uses an anvil to provide increased torque and spin the bit with more power. It is often used in everyday home improvement projects as it takes less effort to drive long screws into the material and minimises the danger of stripping.