Depends. People have a one leg that's longer than another, yet often the difference is indeed small its not necessarily detectable. Definitely, when a large amount, there is more likely to be problems because of the changes in alignment on the spine and also other parts of the body. Certainly in case the difference is a miniscule amount, it is most likely not going to be an issue. From where the debate and discussion is just where is the cut-off point is as to when the difference is clinically significant or not. Some people think several millimeters is significant; yet others believe that its not important till it at least some inches. It is also going to rely on activity levels. Several millimeters may be significant if you run marathons. A number of inches certainly will not be important is you lead a sedentary lifestyle. There may be very little research to guide this method. More information is certainly necessary to base decisions on.