Since their purpose has been mentioned in responses that I received, I notice now that poles on a convex curve often have a push brace pole.
Some of the much older push brace poles have been cut at the top a certain way so to fit directly on the side of the pole that they are leaning on, as opposed to special hinges that are fastened on. They otherwise seem to have a flat roof instead of a gable roof, but with a less hinge-like way of fastening the two poles together.
For a number of years, I thought that the push brace poles were used because of the ground conditions, such as softer grounds.
I also saw another instance in which a push brace pole is used: a pole which has wires that go off to another street that is on the same side as said pole.
I know of at least a couple of rare instances of two push brace poles being used on the same pole. One instance is located in an eastern New York state area; both push brace poles (one tall and one short), are on the same side of the pole. The other instance is located in Montague Center, except that the two push brace poles are about the same size and are each on a different side of the pole.