In Pokémon Red, Blue and Yellow, enemy Pokémon from computer controlled Trainers (but not wild Pokémon) prioritize super effective moves over regularly effective or not very effective/non effective moves even if the move does not deal damage.The AI was changed in Pokémon Gold and Silver so that opponents will not always use a non-damaging super effective moves if no super effective damaging move is known. (e.g. Bird Keeper Jose's level 34 Farfetch'd on Route 27 will not be locked on to Agility against a Zubat)
Example
In Pokémon Red and Blue, all three of Lance's Dragonair know Agility as their only Psychic-type move. Agility is a status move rather than a damage dealing move, however, these Dragonair will be 'locked on' to Agility against a Poison type Pokémon such as Zubat, because the Psychic type is super effective against the Poison type.A low level Poison type Pokémon could eventually beat one of Lance's Dragonair, and the process could be made quicker with a poison inducing move such as Toxic.
As enemy Trainers don't use PP in Generation I, Dragonair running out of PP on Agility is not a problem.