It can also be used for killing someone by spraying onto a person. It chokes them until they are dead, but it isn't very useful for a lot of threats.
It is possible to change the color of a vehicle simply by spraying directly on it (sometimes in diffrent angles because of the size and shape of the vehicle). The vehicle will change colors randomly, no matter if its the color that the vehicle spawns with (or can be resprayed in Pay'n'Spray).
In GTA San Andreas, if the player sprays in front of a mirror, the spray will become invisible.
Since you are able to kill with it, the spray can is technically the first weapon you receive in the game.
It is possible to make your spraycan become unlimited ammo at the very beginning of the game without using cheat codes, trainers or etc.. To do so, keep stocking your spraycan "ammo" from The Johnson House, and after it's "clip" has reached over 10000, it's "ammo" will become unlimited.