Bill Vonnegut offers us a crisp comparison of the difference that the same wave height (3 feet) has with two VERY different swell periods of 8 seconds and 18 seconds respectively. This is often a hard concept for paddlers to understand, and very helpful when planning open crossings and of course surf or rock gardening. 

I usually describe the difference as how much water and energy the wave has (longer period having exponentially more of both), and I feel that many folks find that hard to digest. As always, the “best” height/period combination will be group and site specific, but for surfing on our Long Island play spots, we generally prefer as long a period as we can get (18 seconds is unheard of here) and smaller waves to go with it. On days with very short periods, we need somewhat taller waves to compensate, but that quickly becomes dumpy and no fun.