What is the reason for the Broadway layout style of four bars on a line?
A Broadway show is a work in progress and room must be left for last minute changes, corrections, additions, etc. If music were laid out in a normal, tight format, there would be no room for such changes, which must be physically pasted onto the parts. Although the computer would allow you to reprint the parts, that is usually not an option because they have been marked up by the players. This style also improves sight-readability, since the rule is not strictly four bars on line, but rather that phrases must start at the beginning of a line.
