You just have to use your imagination a little... 
If the market is near the strike at expiration, the position is worth quite a bit of money. For comparison, take SPX and assume at OCT expiration the SPX is at 1350 and you are left with the NOV 1350 and DEC 1350. The remaining backspread will have a huge premium in it for a nice net credit.
THe position does not cost hardly anything to put on. In fact, using OTM strikes I can put it on for a net credit. If the market drops or runs too far up, the position can be closed for a small profit in most cases. If the market is near the strike at expiration , the profit potential is huge.
The position is Vega neutral at inception and a rise in the market results in a drop in IV.
The underlying bet is that the short wing expires worthless and I can close out the remaining backspread for a net credit.
Just test out some scenarios. That is what I am doing today.
One question I still have is whether I can do it for a net credit. I will have to wait until the market opens and see the actual b/a spreads. Also, test the legs for IV changes.
Rally, if the short leg expires worthless and the market rallies huge, assuming I did not close the backspread, the profits are also huge.

If the market is near the strike at expiration, the position is worth quite a bit of money. For comparison, take SPX and assume at OCT expiration the SPX is at 1350 and you are left with the NOV 1350 and DEC 1350. The remaining backspread will have a huge premium in it for a nice net credit.
THe position does not cost hardly anything to put on. In fact, using OTM strikes I can put it on for a net credit. If the market drops or runs too far up, the position can be closed for a small profit in most cases. If the market is near the strike at expiration , the profit potential is huge.
The position is Vega neutral at inception and a rise in the market results in a drop in IV.
The underlying bet is that the short wing expires worthless and I can close out the remaining backspread for a net credit.
Just test out some scenarios. That is what I am doing today.
One question I still have is whether I can do it for a net credit. I will have to wait until the market opens and see the actual b/a spreads. Also, test the legs for IV changes.
Rally, if the short leg expires worthless and the market rallies huge, assuming I did not close the backspread, the profits are also huge.
Quote from rallymode:
It doesnt matter whether we look at the position as a backspread and a short call in the current month or as a long and short calendars. The result is the same. I am still not understanding what the underlying bet is here. It sounds like you are playing for theta and expiration near your short strike, while to me it appears vega dominates the position. I cant imagine the position moving more than 20 cents away from neutrality. You just end up paying the vig on 3 legs. I am deeply puzzled by this position as i cannot understand for the life of me why one would put it on.
Would be nice if riskarb peeked in here and made a comment on this.