You have LH who presumably suggest A/THR off with manual flight.
You have BA who presumably mandate A/THR on at all times.
Go figure.
Since this question is on the use of A/THR in particular, it is worth noting that your understanding of GS mini being lost without A/THR is a gross error. It's just an (automated) speed bug on the dial. No harm done, but uncovering how this mistake happened during your research might unearth a few more.
Take care, feel free to ask.