>>3256736>because film is better overexposed than underexposed people would just put a slower film speed in to make sure they didn't underexpose?Essentially this. It is a safety net for (most) negative film. Also many people like the look of overexposed Portra or Fuji Pro400H.
Lastly, in very contrasty light, when you try to contract a very wide dynamic range to fit into the film's DR, you *have* to "overexpose" film (meter in the deep shadows), and compensate in development to save the highlights (either by reducing dev time or by using a compensating developer).
