The User Manual I have is dated July 2017. It should have been installed when you installed the v3.7 software.
You are correct; they are not related to the LFOs. They are used by the ST3 sample engine (User Manual 5.3.5). The only explanation I have seen is in the ST2.5 manual "SampleTank
uses samples as oscillator waveforms but with a synth engine that is much more flexible than conventional hardware samplers."
My own guess is that few people use this feature with a deep understanding, rather they pick one of the synthesis modes, adjust the controls and see if they like the sound produced.
Sorry, I do not know of any ST3 architecture document.
And your English is fine (unlike the errors in those highlighted sections of the User Manual).