Agitation varies a lot from person to person. It also affects development quite strongly. The object is to find a scheme that works well for you and then to be consistent. The Kodak recommendations are a good starting point. You may, however, have to adjust the developing time a little because of the individual way you do the agitation.
Fixing goes to completion, so agitation has a less noticeable effect. I go the vigorous route in the fix, just to be sure.