Are shield batteries even useful, or should you just build more cannons?

Every Protoss player builds them, but are the shield batteries actually useful cost spending to defend your base? In this video we will find out if building shield batteries is better than building additional cannons. Two cannon lines of 900 minerals defend against 3:3 Zerg, protoss and terran units. Who will win, and are the shield batteries worth it? Starcraft 2 is a real time strategy game developped by Blizzard entertainment. #starcraft #starcraft2 #rts