I recall JB asking once why Star Trek would have filmed wasted footage, and could a table reading not give a good estimate of an episode's running length?
I was just reading about "Let That Be Your Last Battlefield" in These Are the Voyages Season 3. The episode is padded with footage of the two aliens running through Enterprise hallways with memories of burning cities in their minds, as Spock gives a play by play of what deck they are on. This episode ran short when it got to the editing stage and this extra footage was hastily filmed and inserted to get the right running time.
The author then mentions in Seasons 1 and 2 that scripts were purposely 3 or 4 pages TOO LONG and hence about two extra minutes of footage was filmed of scenes that the public never saw, for each and every episode. Decisions were then made in the editing room as to which two minutes were the least important or entertaining, and we never saw them.
But for Season 3, the budget for each episode has been cut, even though the actors all got 10% contractual raises, so money needed to be saved. Season 3 scripts were written to the exact running time, and everything that got filmed was intended to be used.