This is related how server side and Dashboard communicate.
ui_control node sends message on many socket events. (connecting,disconnection,change tab). Here it is not important what is the content of this message (you can get advantage of the message content but this is another story) but the event itself.
Gauge, when initialized has configured defaults. It always starts with configured state. Those are what you can configure from edit panel.
Additional configuration (with msg.ui_control.options) is not stored in gauge. So this must be resent every time after deploy (and/or if you need to change it) And of course the configuration may have totally different in any time. for example if your server running all the time and you just open the dashboard at random time, the gauge also needs to be with up to date configuration to present info correctly.
So at the moment the connection established and ui_control fires the message, that fires your custom configuration to be sent to the gauge.
