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.
A hammer drill contains a hammer clutch or a hammer-like mechanism which provides a circular rotation and a forward driving force. A hammer drill is capable of performing heavy-duty tasks, but it can also be used as a regular power drill.
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.