In Grand Theft Auto: Vice City, tapping the attack button will make Tommy rev thechainsaw, and frighten nearby pedestrians. This can be done both while moving and standing. It can only be done while moving in Grand Theft Auto: San Andreas.
In Grand Theft Auto: Chinatown Wars you can hijack cars in front of police by using the chainsaw on the car. When the passengers walk out, take the car without any worry of alerting the police. However, be careful of accidentally killing the escaping passengers.
In Grand Theft Auto: San Andreas, like the baseball bat in GTA III, you can kill many pedestrians without penalty as long as there is no law enforcement in the vicinity. This can lead to large sums of money if planned correctly next to a save point or a Pay 'n' Spray.
In Grand Theft Auto: IV , a powersaw can be found by workers in construction sites. This maybe would have been in the game as a weapon, replacing the chainsaw, but it was cut.