[ Question copied from https://math.stackexchange.com/questions/2541170/euclid-s-proposition-i-3-overused ]
Although the references to postulates, axioms, and previous propositions are not part of the original text of Euclid's Elements, all the editions I have seen contain them.
In many propositions, it is needed to make adjacent segments, say $PR$ and $PQ$ equal. Examples include:
All the editions linked from this page and more (I do not have enough reputation to post the links to them): John Casey’s English translation, Richard Fitzpatrick’s edition, Johan Ludvig Heiberg's edition, and Józef Czech's Polish translation refer in those cases to Proposition I.3, which is about making arbitrary segments equal (“To cut off from the greater of two given unequal straight lines a straight line equal to the less”).
As I understand it, for making adjacent segments equal, Postulate 3 (“Let it be postulated to draw a circle with any center and radius”) is sufficient. Why do all those editions of Elements refer to Proposition I.3 instead of Postulate 3 in the propositions I listed above? The only reason I can think of is editors' inertia.
[I am not asking about uncontroversial uses of Proposition I.3, like Proposition I.6, where $DB$ is made equal to $AC$.]