mirror of the concept art on DA:

Physically weak, lightly shielded and armoured, but with strong sensors these units rely on stealth, speed and the protection of others to perform their tasks.

They function as engineers, infiltrators and saboteurs or snipers.
So their general tactic is to hang back or hide, providing other units with reconnaissance, or taking out critical targets from range. They also perform in field repairs on whatever equipment as necessary. Some even are trained to function as medics or tactical advisors.