Re: New Book about TOS: These Are The Voyages
They did a ton of location work, and the cutting of Mission: Impossible was faster than just about anything else on television (which meant more set-ups). It was also a series dependent on a lot of detailed insert shots, which were often shot later. Basically, the show took a lot longer to shoot than it was scheduled for.
EDIT: What Warped9 said, essentially.
Yes, but you've expressed it better and more succinctly.
STAR TREK: 1964-1991