Sometimes you may see a photon cannon used to deny an enemy's natural expansion to try to gain an economic advantage. Depending on the map and matchup, it may also complicate the enemy's early attempts at scouting and aggression.
Typically, you don't see more than 1-2 photo cannons, because you don't usually want to "over-invest" and lose what advantage you gain.
Typically, you don't see more than 1-2 photo cannons, because you don't usually want to "over-invest" and lose what advantage you gain.