Lasers in Space
The various Star Wars fighters (e.g. X-wing, TIE, Death Star) fire laser or pulsed laser cannons. In "Star Trek," the Enterprise fires its phasers at enemy space ships. In both "Star Wars" and "Star Trek," people fire hand-held laser or phaser weapons. In all of these scenes, we see the laser beams travel and hit their targets. The problem with this is that you cannot normally see a laser beam.
A laser is a highly focused beam of light with the photons traveling in one direction. None escape to hit your eye and make the beam visible. In a vacuum, you would only see the beam light up where it hit the target (light is scattered by the matter in the target). There is nothing in the path to make the beam visible. You can demonstrate this with a laser pointer or flashlight in a clear room. Point the laser/flashlight at the wall and you will only see the spot on the wall. To make the beam visible, you must place fine particles in its path to scatter the light (such as chalk dust or baby powder).
I don't know of even one sci-fi film or TV series that demonstrates the proper functioning of the laser beam. Most make the beams visible through special effects because it would be unsatisfying for the viewer to see a character fire a laser and not see anything.