Brian De Palma's classic 1976 adaptation of the Stephen King novel remains unequaled despite the occasional unnecessary attempt to remake a movie that was perfectly good the first time around. He utilized slow motion in the opening locker room sequence, to lull the audience into a false sense of security via sexualized voyeurism—which takes a sudden turn into the horrific when Carrie discovers she's having her first period and thinks she's sick or dying, having never been educated about menstruation by her overbearing mother. Her cries for help are mocked cruelly by her peers, and as she lies humiliated on the shower floor, we see the first glimpse of her telekinetic power in an exploding bulb.
In many ways, this scene is a parallel to the climax, when Carrie is crowned the prom queen. Slow motion gives the scene its emotional resonance, appropriate for the heightened feelings and sense of significance in the world of high school. In what would have been only a few seconds of real time, we dwell on Carrie's long moment of pride and happiness, the leering anticipation of those who scheme against her, the mounting suspicion of her friend Sue, the fall of the bucket of pigs' blood, and finally Carrie's confusion and humiliation as she looks over the sea of mocking, laughing faces. For Carrie, this is the moment of true horror—a moment De Palma executes perfectly.
Then, of course, time catches up with us as Carrie unleashes her telekinetic revenge upon those who tormented her, portrayed by De Palma with the now little-used split-screen technique and sharp, almost reptilian reaction shots of actress Sissy Spacek. This wonderful contrast gives us the visceral feeling the game has changed, and so it has. What would have been a completely discombobulating scene overall if shot in real time is instead allowed to linger, for the audience to truly understand Carrie and her desire to kill them all. We get it.