A standby switch supposedly enables heaters to run [often at a lower voltage] while the ht is switched off so that everything is warmed up ready for the ht to be applied. When ht is in fact switched in, you can get a lot of noise as all the voltages set themselves up very quickly rather than slowly settling as the amp warms up if switched on from cold. This causes a worrying `whumpf` and odd glow from the valves.
The Triode/Ultralinear switch is another dubious one because a circuit is either optimised for one or the other. Such amps often sound worse in triode mode giving a softer focus and a slightly echoey effect which some interpret as greater depth. Ultralinear has more leading edge bite. Even with the 104db Loth-X Polaris, they don`t respond to triode mode on most EL34 triode/ultralinear switcheable amps – just sounding more round-shouldered and wishy washy.
Yet reviewers extol these gimmicks as if they are the way forward.