By default the application launcher is called with Super + Space and Alt + F2. (It can be changed.)
But there is a difference; after showing the Applications launcher, the Super + Space shortcut also hides it if pressed again; Alt + F2 doesn't do that.
And neither do other shortcuts:
The same difference is present if the default shortcuts are changed as indicated in the answers to the linked question: the launcher is shown but not hidden with just the Super key (unlike in Ubuntu Unity). That is my main reason against giving up the default Super + Space shortcut in favor of just Super on elementary OS.
What is special behind Super + Space ?