This is a distinction that mattered quite a bit more in the 80s, and still matters today in limited application. While the comment in that is correct (return fo

This is a distinction that mattered quite a bit more in the 80s, and still matters today in limited application. While the comment in that is correct (return for multiline, and enter for selecting default option) a key feature for the macintosh, and any computer of the era, would have been being used as a terminal emulator (console for a mainframe or server of some sort). On line based serial consoles, like interacting with a PDP or VAX (common in the era), you would be emulating a teletype. Return is short for "carriage return", physically moving the cursor to the head of the next line. In use cases such as that, enter doesn't matter as much. However, on many IBM computers, where the UI is form based (not line by line serial as many expect): return is for new lines only or moving to the next form field, and enter is for submitting the whole form as is. You still see return vs enter on modern keyboards, usually in the numpad area. TLDR: it was probably considered a necessary function key for interacting with non-macintosh computers, a substantial use-case in the 80s