Retake if 1400 falls below the middle 50% at schools you seriously want, if your colleges superscore so a second sitting can only help, or if a scholarship threshold sits just above your current score. If none of those apply, your time is better spent on essays and the rest of the application.
1400 is the score where a retake most reliably changes outcomes, because it sits below the middle 50% at most selective schools while being comfortably within reach of 1450 or better. The caveat is that a retake only pays if something about your preparation changes; sitting the same test again after the same preparation usually returns the same score.
The full picture, with the surrounding detail, is in Is 1400 a Good SAT Score? Strong Outside the Top 20.