Delivering electricity to homes through high voltage lines, reduces the power loss that is caused by Joule's heating.
We know that:
P=VI
Where, P is power, V is the voltage and I is the current.
So if we keep P constant and make then voltage up, I must goes down.
According to Joule's first law : Power of heating generated by a conductor is directly proportional to the product of its resistance and the square of the current.
Now using the equation:
Q=I²Rt
Where Q is the heat generated, I is the current , R is the resistance and t is the time.
So by reduced I, heat loss will be reduced.