Today's EW.com poll was on mid-season finales. (I voted 'yes', as you can see.) Funny thing is, I was just thinking of this last night as I watched the Once Upon a Time mid-season finale.
At first, I thought it was just to build hype. To get people to watch. To build some sort of suspense. It's just a ploy on behalf of the network. It doesn't mean anything except to draw us in. (And, for the record, that 'no' choice was winning this poll with 64% when I voted.)
But then I got to thinking about the old debacle of Lost and the season that showed a new episode and then a couple repeats and then another new episode and how much it SUCKED. And how the next year, when they announced that they would show consecutive sets of episodes, but with a HUGE break in between, people were horrified. (people = me, in this case)
Then I got to thinking about one of my all-time favorite episodes of Lost - the 3rd season's 'I Do.' The episode was to serve as a 'mini series finale' before the break, ending with the cliffhanger of Jack yelling, 'Kate, damn it, run!' over his walkie, mid-surgery on Ben.
I'm not saying Lost is the first show to have a mid season finale..... but it's the first one I remember. And Lost is one of the first shows I recall showing two blocks of episodes with a long break in between.
Nowadays, that's the norm for most longer series (not cable shows like Mad Men, Justified, Boardwalk Empire, etc that usually only have 12-episode seasons to begin with). Premiere in the fall, break for the holidays and come back in the spring.
The key there is 'come back' - shows need to do something to get fans excited enough to come back after months of waiting. It isn't just the network labeling the show a 'mid-season finale'. It isn't just the network adding suspense with that title in the commercials. It's the episode itself. IT needs to be suspenseful. It needs to draw people in and get their attention.
In fact, I bet that if you watch a bunch of older series on DVD, you wouldn't be able to pinpoint a mid-season climax, but with most new series, you would.