Quote from RedEyeFly:
I would not do this trade for the simple reason of term risk. If vols explode in AUG or SEP the front month is going to go absolutely bananas (which you'll be short) and the back month will probably remain a bit more tepid as it will be pricing in the next 6 months of mean revision vol which will be expected at that time, no matter what the market is doing.
Consequently, its actually possible that you could LOSE money on this trade, depending on how your weighted vega is calculated. Chances are you won't lose, but your profits could be quite a disappointment.
The only reason I would do this is the following. There are instances when I have decide that an underlying would go up or down to a particular price and then stay there. You can buy an OTM calendar with the front month in a near term and the back being way out or even a leap. If your market prediction is correct AND you plan to hold the position to the expiration of the front month, AND the market sits for a long time after the move, you may have a nice opportunity to sell many many expensive front month calendars spreads against a once very very cheap back month. I used to do this on both sides of GOOG because if you're correct you could possibly make 10:1 or better. You'll need to plan to roll around a bit to keep the back month in play, but all in all, a lot needs to happen in your favour in order for this to go off without a jumbled mess.
No matter how you look at it, it's a crash or sell off spec play - not crash protection.