In what ways do "Launch Game" and "Standalone Game" differ from an actual build?

Couldn’t find an appropriate place to post this, so I’m posting it here.

In the UE4 editor you can choose an option to play the game as a “Standalone Game”. Or, if you right-click your .uproject file, you can select “Launch Game” to play the game. I’m assuming these are pretty much the same.

How do these things differ from an actual build of the game? Are they fairly-reliable representations of what you really get in a build? I’m guessing they must be at least somewhat different since packaging takes a long time and “Launch Game” doesn’t