What is the advantage of using series parallel connection?

Series connection has only a single path through which the electron can travell,where as the parallal connection has many paths to travell the electrons.So in a serise connection if one of the component of the circuit is switched off,every other component of the circuit will be switched off.

Fairy lights are usually series connected. The main voltage is divided across the number of lamps. So each individual lamp is low voltage.