Increased Capacitance
Capacitors use dielectric materials to increase their charge storage capacity. The dielectric material dissipates charge at the same rate as the plate charge, allowing them to store more charge.
Voltage Rating
Dielectrics increase the voltage stress resistance of the capacitor, increasing its storage capacity. This is important when high voltages must be handled.
Energy Storage
Capacitors store more energy because they have higher capacitance. This is especially important in applications such as power supplies and energy storage systems.
Insulation
Dielectric materials are insulators that prevent charge from reaching adjacent plates, allowing the capacitor to function properly.
Reduced Size
Dielectrics increase capacitance, allowing capacitors to be smaller in size. This is useful in smaller electronic devices.

Dielectrics improve the overall efficiency and effectiveness of capacitors in a circuit.