Step-Down Regulator vs Serial Regulator and Switch Mode Power Supply

Why do we use step-down regulators rather than using serial regulators or switch mode power supplies? Are they more efficient? Or do they have any other advantages?

Hi,

By "step-down" you mean a buck circuit? That's a switch mode circuit too.

Switch mode circuits are much more efficient than a series regulator when there is a significant difference between the input and output voltages.