The Robotics Facility (or Robo for short) allows the production of Shuttles, a flying transport unit which allows the player to bypass cliffs and access islands. It also allows the construction of more advanced robotics buildings: the Robotics Support Bay and the Observatory.
With the appropriate expansion buildings, the Robo enables to Protoss player to produce Reavers, an extremely useful Protoss unit capable of heavy support, harassment, and sieging, as well as the Observer, a cloaked flying unit that is very useful for scouting and detection.
The Robotics Facility is very useful as the Shuttle and Reaver form an extremely effective combination which is used in all three Protoss matchups, while the Observer is vital to serve as a mobile detector.
The Robotics Facility does not research any upgrades, but its Plasma Shield can be upgraded at the Forge.
In terms of competitive usage, the Robotics Facility is generally constructed in all three match-ups, for both offensive and defensive strategies.
In the PvT and PvP match-ups, the Robotics Facility is built fairly early on to build Observers. Shuttles and Reavers are also commonly employed by the mid game. During the early game, the Protoss player can sometimes be seen building a Proxy Robotics Facility near the opponent's base to allow a speedy and surprising Reaver drop attack.
In the PvZ match-up, the Robotics Facility is commonly built by the mid game to build Observers. If the Protoss player opts for a Reaver-intensive attack force, two Robotics Facilities may be built to maximize construction of Reavers and Shuttles. In the late game, the Protoss player will often build a Robotics Facility at vulnerable or distant expansion bases, thus enabling the local production of Reavers at the expansion base. This lessens the burden of the Protoss player having to continuously move troops to the expansion base.