Ground losses in mains delivery network
The neutral wire is not a perfect conductor, so the earth will carry
  some current. There must be some loss, by definition.


For a single phase supply, the neutral wire will carry the full-load current and let's say that the wire resistance between load and pole transformer is in the region of 0.01 ohms. 

So, if there is 100 amps, the neutral wire losses are 100\$^2\$ x 0.01 = 100 watts.

If the neutral wire is grounded both at the load-end and at the pole-end and that earth ground is (say) 0.1 ohms, the net impedance is 0.01 || 0.1 ohms = 0.009 ohms. With 100 amps flowing the losses are 90 watts.

In other words, the grounding makes the impedance lower and losses are reduced.



As far as I'm aware there are earthing points on poles carrying transformers but it's unclear whether there are also earthing wires on poles that don't carry ancillary equipment. I can't be 100% sure but I think I've seen earth wires on plain ordinary electric poles. Maybe it's different in different countries and regions?