The Standby switch on Bugera Amplifiers is used to to stop audio passing to the outputs of your amp, similar to how a mute button would work. 

What we would recommend is ensuring the Standby switch is engaged at 1st power on for roughly about 5 minutes before use, to ensure that the valves have time to warm up before operation. 

It is ultimately down to your own personal preference how you use the Standby switch.