Indicate left after overtaking, or lane change on a motorway

[Jon39]

This might now be taught during the driving test, but I only indicate left when the move needs to be communicated to following drivers. Am I correct?

An example where to me, it would appear to be unnecessary.
Light traffic on a motorway. You indicate a move from lane 1 to lane 2, in order to overtake a large HGV. After the overtake has been completed, and there is generous space in front of the lorry, I return to lane 1 without indicating. The only vehicle of concern is the HGV which I have just overtaken, and that can hardly be expected to quickly accelerate to close the gap between us.
Some drivers do indicate left after such a manoeuvre, and I wonder why they do it.

Any comments?

[Jon39]

Muddle238 said:

As such, if I have drivers following closely behind, I will promptly pass traffic but I won't indicate back in, as the amber flashing light on a car seems to mean the same thing as a green traffic light to some drivers, who will start closing the already small gap even further through impatience. If you don't indicate, and just move back, you effectively catch the following drivers by surprise and give yourself more space to move back without them registering that in a few seconds they'll have a clear lane ahead.

Here is a technique which I sometimes use, when in exactly the situation you describe. Overtaking a line of traffic, outside lane of motorway, a vehicle behind appearing to want to overtake me at the earliest opportunity.

Reduce speed slightly, but still going faster than the line of traffic being overtaken. If applicable that should create a greater gap ahead of my car. Just before the point of completing my overtake, whilst still going in a straight line, accelerate hard and create a much bigger gap to the vehicle following. Then complete the manoeuvre by reducing speed and returning to the inside lane.

The following vehicle has been unable to undertake because of the line of traffic, and it ensures I can keep well away from the following vehicle at the moment it passes me. Obviously a car with an 'adequate' reserve of power is needed to do this safely.