Quote from smilingsynic:
For calendars, I prefer to use calls over puts (even though doing it with puts tends to be cheaper), but riskarb is right: you're just doubling up. Either way, you win on a little/no movement, and lose on a lot of movement.
Now if the calls that were being sold (1) were at a different strike than the calls that were part of the short straddle (2), that might be a different story (skewed options due to supply and demand). If the calls (and the puts that are part of the straddle) are from the same strike and expiration, then there is no edge.
Why not? Calls and puts at the same strike trade at the same implied volatility. If your computer model does not recognize that, then it is using incorrect/stale data. If they traded at different iv's, there would be a risk-free arb.
Besides, with just the calls, you are dealing with two b/a spreads and two commissions (short call, long call) ; with straddles you're dealing with four spreads and four commissions (short call, long call, long put, short put). And all for nothing.
Why would anyone want to do that?
I agree that both strategies will have the same results over a long time period,but not month by month my statedly sharpe ratio(piece of mind for me)will be lesser also do weekly ratio's adjustments according to changes in XYZ , Gamma and Theta.If I will go with Calls(or Puts) only,I will lose the flexibility here,especially if XYZ's move in the first week after position taken am not trying to convince you here,I am just showing what works for me(so far).