I have been buying Calendars right before earnings depending on the outlook for the underlying and which options offer the best chance of profiting. The Calendar spread is of little value to me per se other then to capture high front month IV. They are sold after the collapse--not held to expiry. Typically, the best opportunities have arisen from at least a 10% Vol difference. Dbl Calendars are usually redundant but come in handy for stocks like ISRG and MA. This earnings season 76% of my Calendar trades made at least 50% on risk although there are only about a dozen Dbl/Calendar trades thus far. It is a nice little spread that comes in handy. Using this setup properly improves your overall risk/reward/prob. I'm hopeful that other option traders can expand on this basic approach. Floor traders say that the consistent trader will be the next to blow up.