Answer :
If you have a light bulb and you want to be able to switch it on and
off, then you must connect the switch and the light bulb in series
across the battery.
If you connect the switch and light bulb in parallel across the battery,
then the light bulb will shine all the time, and PLUS ... when you flip the
switch to ' ON ', sparks will shoot out of the switch, the wires will get hot
and smoking, and the battery will instantly empty itself.
So this is an application where the series circuit might work better than
the parallel one.
Another example could be Christmas tree lights. You have sometimes hundreds of lights wired in series. If they were in parallel the wire would then have to go to each light meaning potentially hundreds of different wires
