Here is an excerpt from an article I found online. I hope it is helpful:

"Regardless of direction, it is necessary to control your boat speed and choose the one speed at which the boat becomes most responsive and controllable. Going too fast in a following sea means that you'll fly off the top of one wave and bury the bow into the back side of the next. That's not good, so we need to find the right speed which yields the most comfortable ride while still keeping good control of the boat.

When following seas start to get really big, we have only two choices: either we slow down to the appropriate speed, or we have to change direction. If we put the seas on the aft quarter we can maintain a higher speed without stuffing the bow into the backside of a wave. On the other hand, we may not end up going in the direction we wish. (And here you may have thought only sailboats engaged in tacking) It then becomes a matter of whether our higher speed makes up for the extra distance we have to travel. Often times it does, making it advantageous to alter course 20-30 degrees."