They are traditional for overhead runs between house and barn... and much else... on the customer's side of the meter.
The NEC does not cover Poco rules.
And the Poco rules dictate everything from the Service back up the line towards their distribution drop.
This is one area where a j-man has to make both inspectors happy. (County inspector & Poco inspector)
Out my way, the Pocos reject all manner of gear that qualifies by the standards of the NEC. (EUSERC)