What is a common use for a flat screwdriver?

A flat screwdriver is specifically designed to drive screws that have a straight slot in their heads. The blade of the flat screwdriver fits snugly in the slot, allowing the user to turn the screw efficiently, whether it's to tighten or loosen it. This design is simple and effective for a wide range of applications, from assembling furniture to fixing appliances, where such screws are commonly used.

While removing torx screws requires a different type of screwdriver that fits the star-shaped socket of a torx screw, and creating leverage involves using other tools or techniques, the primary and most recognized function of a flat screwdriver remains driving screws with a straight slot. Tightening cogged wheels would typically require a different tool or method, as cogged wheels are usually designed for interlocking and turning rather than for use with screws.