What is the most suitable application for 3mm and 5mm orbit ETS 150 sanders?

The 3mm versions (ETS 150mm Brushless Random Orbital 3 mm Sander) are for fine and extra fine sanding – best surface quality.
The 5mm versions (ETS 150 mm Brushless Random Orbital 5mm Sanders) are for sanding where more material removal is required.

The 5mm could be used in the preparation stages where more coarse sanding is requied.
The 3mm would be used in finishing stages.