someone in the replies elsewhere pointed out that Ctrl+J = 10 in the ASCII table = LF ("line feed") = Enter (because J is the 10th letter of the alphabet)
so Ctrl+J is the same as pressing enter
which I don't have any practical use for but is kind of cool
(edit: some corrections in this reply: https://pgh.social/@ben/112752235264922484)
@b0rk that sort of thing had some meaning when one worked on an Apple // or similar