Depends on your ball flight, the ball, spin, etc. If you hit the ball low, it's less likely to be affected by wind. If you hit it with less spin, also less likely to be affected. Higher spin balls will be more affected. Also, with modern multi-layer balls, shots hit very solid--in the middle of the clubface--are going to be less affected also.
Also, a tailwind doesn't have a directly proportional affect on distance that can be translated from MPH to yardage. A steady 10-15 MPH tailwind will be very helpful for distance, but a strong (30 MPH +) tailwind might actually rob the ball of spin, which will knock it down early.
Wind is all about feel and experience. You just have to play in lots of different kinds of wind to know how it's going to affect your shots--and even then, you never really know. Look at the pros--when the wind is up, they can put up some pretty amateurish looking numbers. It's one of the reasons why golf is hard.