Switchable Tetrode - Triode please explain

It's all inside the tube logic:

Tetrode mode is needed when the dynamic music needs to be reproduced: large orchestras, brass bands and has certainly larger gain than triode.

When the triode mode is used when you need maximum transparency listening to the small instrumental bands, vocals.

Also VTLs having that switchable feature can be used to match different types of speakers depending on their efficiency.

Do not forget to turn it completely off before switching modes!!

If I do not power down the amps I can hear and see how speaker drivers are poppin'.
just don't like to have my speaker blown. even when I place a cartridge needle on the groves I do mute my phono before.