Hmm...here are two tips regarding screenwriting I found on another site--and my take on each of them:
They say: Don’t include a synopsis or character biographies with your
script as it gives studio readers an excuse not to review the whole
screenplay.
I say: When I was a reader, sometimes we'd get these, but it would turn out, for example, that the protagonist's bio would say something like "Paul is a witty intellectual" but in the script there would be no sign of wit. And sometimes the synopsis would not match the script either. Including these is unprofessional, but no reader I know would use them as an excuse not to review the script. They would just ignore them and read the script.
They say: Don’t put scene numbers on your script until it is sold. This is a rule of the game; readers find scene numbers distracting and use them as an excuse to dub a screenplay “amateur” and unworthy of further consideration.
In my experience, some people like there to be scene numbers in a spec script because it makes it easier to discuss which scenes have problems (e.g., in scene 43 the action slows down). No reader I know would be distracted by such numbers nor dismiss a spec script because it has them.
Maybe the person who wrote these tips heard different, but beware of believing such "rules."