Meaning - it's over, ended, finished - therefore, time to go home.
From the days of Elvis concerts when the crowd would cheer for encore after encore, it was necessary for the compare to announce - 'Elvis has left the building.'
For grammar lovers, it's a good example of present perfect - he left in the past and it has an impact on the present - he left the building, so he's not here now.
How true indeed. Luckily, there are still plenty of videos around. Everybody has their favorite Elvis song and this isn't mine but I prefer to remember him in his most youthful days.
Is this camp or what?