Well if you have for example call spreads that you write on $100 stock. So you write $110-$115 that means that you have 10% insurance from an up movement in the price from $100 to $110 before you start losing money.
If on FB and TWTR for example today I have around 7% insurance against a move in around two weeks which is holiday weeeks and I think it's a good bet.
Also the math formula picked those two so I'm happy with it :)