Help a girl with her electricity please?

[Skvez]

For the same POWER of unit running at 12V (rather than 230V) it will draw 19 times more current and so will need cables much thicker cables (not exactly 19 times as thick but think MUCH thicker). This is the main reason why we use 'high' Voltage.
When we discuss LED lights this doesn't really matter but once you get into discussing 'white goods' it does matter.

Then you need to consider Voltage drop.
A 2.4V Voltage drop across a cable when you are feeding in 230V (and getting out 227.6V) is tolerable.
Doing the same at 12V in and 9.6V out is not tolerable so you need to uprate the cable again!

Low Voltage means very heavy duty (expensive) cable.