What does Airplane mode actually do and should it automatically be on?

[4lt3r3d]

I noticed that all of my flyouts stopped working except the bottom taskbar volume, caps lock & num lock. So I went into settings to see if I could fix it and noticed that Airplane mode was toggled on. Is it supposed to automatically be on or no? When it's on does it prevent the flyouts from working or does it mute the volume? I don't know whether to keep it on or not.