We don't shoot in lots of 6 or 12; we shoot 22 episodes straight
through. The order in which they are run, and the pauses in between, do
not in ANY way reflect the time period in which they are made. We shoot
straight through, with pauses for Christmas break, and to give our crew
and cast a one-week hiatus on either side (usually between episodes 8
and 9, and episodes 15 and 16), which helps keep them from burning out.
You really have to shoot straight through, because of the vast
amounts of money required to rent equipment, pay salaries for crew and
cast, pay staff and other areas. Also, under Screen Actors Guild rules,
if you hire someone for, say, 13 episodes, you must use them within a
particular span of time. If you don't, you must pay them the balance of
committed episodes by the end of that period. If you broke filming up
as you suggest, you'd be in deep hock to your cast.
And you really can't separate out SFX from shooting live-action;
often you need to have the actors work with the effects in composite
shots, and sometimes you need the effects to play on monitors visible on
camera when you're shooting. All divisions are working at the same
time, straight through. You need to have effects people around frequently
while shooting; to make two separate sequences means you double the time
period you have to pay your effects people.
Here is the process of making B5 in metaphor...not only in terms of
each season's production, but the history of this show overall.
You hitch yourself to the front of a train. And you begin pulling.
(In this case, I began pulling in 1987, but for purposes of the current
discussion make that the start of each season.) Slowly, painfully, the
train moves an inch. Then another. Gradually, over time, it begins
picking up speed. For one brief instant there is an allowable moment of
joy when both you and the train are going at the same, comfortable speed.
Then it starts gaining on you, and you have to start walking faster, with
the train bumping your heels, until finally you're running flat out,
because you know that if you so much as stumble once, the train will roll
right over you.
Then the season ends, you get to catch your breath...and start it all