Some films (which I've never used, having also lead a sheltered life) have a lot of dye in the anti-halation backing which has to be removed. If you don't prewash these, the developer (and, possibly to a lesser extent) the fixer will become coloured. As far as I know, this wouldn't have any effect.
The arguments for pre washing otherwise revolve round getting the film wet (to avoid air bubbles) and getting the film and tank up to developing temperature.
Like others, I've never prewashed.