These units are the workers of the Protoss.The probes has some advantages; the primary advatage is its unique constructing ability.The building is automatically constructed when a probe only sets the building’s place.The second advantage is its speed.The probe is faster than drone or SCV which gives the player a good recon chance.The third advantage is its refreshing shield which can be useful at recon fightings.If your micro is good you can kill some enemy workers without probe loss.