What are the benefits of using a capacitor in transmission lines?

Capaiter is used normaly control the power factor-Loses.Capacitors can be used to decrease the inductance of power lines (series compensation), and for voltage support (capacitors are put in parallel with the system).
Capacitor Control is usually done to achieve as many as possible of the following goals: Reduce losses due to reactive load current, reduce kVA demand, decrease customer energy consumption, improve voltage profile, and increase revenue.
Indirectly capacitor control also results in longer equipment lifetimes because of reduced equipment stresses.

Use for the voltage cobtrol

1- improve voltage levels

2- reduce line losses

3- enhnace the power factor

Capacitor bank is used to even out the electrical fluctuation. Also it helps in providing constant voltage when operating on AC Supply. During the time of zero voltage in the AC cycle, the capacitor bank provides the potential difference.

To reduce transmission loss by voltage drop in line loss

Our practice is to install shunt Capacitor e bank with the load.
The main function for the capacitor bank to enhance the power factor for the power supplied from a transformer/generator.

the simple response and without looking in google and do copy and paste is : the role of capacitor in transmission lines is the Compensation

Mainly the capacitor installed to enhance the power factor in the circuit , since he reduce the reactive current losses and control the voltage drop by improving it .

as in transmission , we have to maintain the value of reactive vars for losses control. therefore for too many inductive vars due to inductive load , we use capacitors as leading vars producer in the circuit. thus we are controling the value of reactive power in transmission and hence losses are controled.

Capacitor banks should always be in consumer side. in low voltage systems.