My copy of 'Airbus Industrie A320 Family Instructor support' 2001 states on page 68:
The GS mini guidance has 3 major benefits:
1. It allows an efficient management of the thrust in gusts or longitudinal shears. Thrust varies in the right sense but in a smaller range(+/- 15% N1) in gusty situations which explains why it is recommended in such situations.
2. It provides additional but rational safety margins in shears.
3. It allows pilots "to understand what is going on" in perturbed approaches by monitoring the target speed magenta bugs: when it goes up = head wind gust.
(all punctuation and bold is Airbus').
Then there follows an explanitory diagram, and the text below that states:
........We can notice that in between a) and b) we have a front [20 kt] gust. We shall see on the PFD speed scale the target speed going up from 137 kts to 157 kts, while simultaneously the speed trend arrow and the IAS will go up for obvious aerodynamic consequences; the thrust will increase, but not excessively because of the speed trend already experienced.
And finally a diagram showing the PFD speed scale annotated with:
Head wind gust
IAS and speed trend arrow go up, target speed goes up and N1 smoothly increases
(Airbus' bold again, but all quotes hand typed by me)