[m463]

I always use cmd-o - never knew about cmd-down - it seems to do the same thing - why a different keystroke?

[qubitcoder]

Same here. I just learned about Cmd+down today after using macOS for nearly two decades. I've always used Cmd+o (as in, "open").

But it makes sense. Especially when considering that an Application on macOS is basically a folder (e.g. right click on an app, and select "Show Package Contents"), so navigating "down" into an app would open it.