Bunkers constitute solid base defenses, but they can also serve as offensive tools. After locating the enemy base, send a small infantry strikeforce accompanied by SCVs. Build bunkers on the perimeter, load your troops in, and use your SCVs to repair any damage they sustain. This is a useful tactic in the early game to pressure your opponent and force them to cancel their early expansion, or to earn a quick victory by bunkering up to the mineral line.
Scouting your base's perimeter is key to stopping this tactic. Just set up patrols outside your base or have units, or structures, to give you vision. If you spot it in its early stages, you should be able to stop it without too much trouble. This also applies against protoss players trying to box you in with photon cannons. Do not be afraid to pull your workers for additional stopping power. Though pulling five or six workers will cost you a good deal of mining time, it’s worth it to prevent the enemy from taking out your expansion.
Offensive bunkering is not limited to the early game. It usually is a good idea to support your forces with SCVs, and build bunkers in the enemy base to give your infantry another layer of protection, as well as added attack range.