The Goliath is a Terran unit that is constructed by a Factory after the construction of an Armory. Although the Machine Shop add-on is not necessary for the Goliath to be built, the attachment is necessary to gain access to some vital upgrades.
The Goliath is most useful for its powerful anti-air attack, although it can attack both air and ground targets. It has high range and deals substantial damage to the opponent's air units. Furthermore, the Goliath's air attack can be even more effective once it is upgraded. This longer range attack meets or out-distances all air-to-ground units in the game.
Dispatching some Goliaths with the Terran Siege Tank push can be particularly useful for preventing drops on the Tanks while they are in Siege Mode. Further, groups of these units can be used defensively against massed a variety of air units.
The Goliath's air attack is actually two simultaneous rocket attacks, meaning a unit's armor should be counted twice. In addition, it is an explosive attack type, so it does 50% damage to small units, 75% damage to medium units, and 100% damage to large units, meaning it is most efficient against heavier air units. but it still can be used to great effect even against Mutalisks and Scourge, small units, as can be demonstrated by professional play.
Researched at the Machine Shop.
Goliaths, while potent, are very bulky in their movement. The are cumbersome in turning about and can be impeded by one another when moving in a group.
Goliaths are generally built in the mid to late game. They are used in conjunction with Siege Tanks, and sometimes Vultures or Valkyries in mech or mech-bio TvZ variants. The Goliath's purpose is to help stifle the Mutalisks. While Goliaths are relatively immobile compared to the Marine and Medic combination, its superior range and damage compensates. Goliaths high rate of fire and high health make them fare very well against Zerglings. Also, they have vastly longer range than Mutalisks which allow them to micro to some extent. Hold position micro is useful against enemy Mutalisks while running away to use the Goliaths' superior range.
Goliath, Vulture, Siege Tank "balls" (i.e. Units surround each other, providing simultaneous attack and defense capabilities to one another) that are fully upgraded are particularly challenging to stop.
With the advent of the Fantasy Build, involving an early mech strategy of both harass and anti-air defense, Goliaths became more and more common on the TvZ battlefield.
Goliaths are used to help stop early Wraith attacks and are very good against Vultures with Spider Mines due to their range and damage. Goliath and Seige Tank drops (particularly in large armies of 8-10 Dropships) comprise the majority of late game drops as the two make up a potent combination of anti-air and anti-ground attack. Commonly, drops have a Goliath or two in them in order to shoot down Wraiths or even approaching Dropships.
Some Terrans may also choose to harass the opposing player's economy with Goliaths. Because four Goliaths fit inside a Dropship, Goliaths are fairly efficient at killing SCVs.
Being the premier Terran anti-air unit, Goliaths are seen at least in some numbers in virtually all TvPs where the Protoss decides to use air units, which is often at least for Observers. It is common for the Terran player to see the faint outline of an Observer to move a few Goliaths in that region before running a Comsat Scan to reveal the Observer.
Goliaths are sometimes seen in small numbers during the mid-game to pick off Shuttles and Observers. When facing Arbiters on the field a handful of Goliaths are useful to snipe them or force them back. Against Carriers, Terrans will generally pump mass Goliaths as their long range and high damage are the best deterrent to Protoss air. To provide further support to its Goliaths, the Terran player will sometimes shield the Goliaths at the forefront of the attack with Defensive Matrix.
A notable build for TvP that utilizes Goliaths is the Flash Build. It involves upgraded Goliaths and was engineered to stop the Carrier builds on Katrina, which features many cliffs, ramps, and other obstructions for ground troops.