The reason for this is that if you do not take a reading the electricity company will bill you from the last reading of the previous occupier.
Even when there is an advanced meter at the property your electricity company will not take a reading and bill from that, they will still bill you from the last reading of the previous occupier.
Whilst this would be fine if you moved in the afternoon that the other person moved out, in practice this doesn't happen.
Also most people don't turn their electric hot water cylinders off after moving out, so unless you take a reading you will pay for the electric hot water cylinder heating that occurred between the last occupier moving out and you moving in.
This assumes that the reading the last person gave was accurate (unlikely as you give misleading readings and they won't be caught). It also assumes that nobody did renovations or cleaning in between occupancies. It is just too risky not to take the reading when you move in.
Unless you give this start reading the day you move in you can easily wind up paying for usage that isn't yours, and the electricity company will not do much about it.
To bring home the point further we'll tell a brief story about our sales manager when he was working for an electricity company. A lady rung up to give her start reading, which was just over 1000 Kw different to the final reading of the previous occupiers. Our sales manager queried this and confirmed she was reading the meter correctly. He explained that this was a lot of usage different and asked if anything had been done on the house in the meantime. The lady said that the previous tennant had flooded the house and done a runner (but closed their electricity account) and the landlord had had 5 industrial dehumidifiers and 10 industrial fans running for the past 10 days to remove the moisture.
That phone call saved the lady hundreds of dollars.
Next time it could be you, call your power company when moving into a new place, and give them that reading.