The diagonal row of zeros shows, of course, that if you replace an old fork with a new fork of the same length, there will be no change in head angle. If all else remains the same, a steeper head angle is quicker handling, while a shallower head angle is slower handling. I've changed the color of a few values in the table to red. These are the changes in head angle that are greater than half a degree in magnitude. I've made them red because, in my experience, any change over half a degree will probably be noticed.
Some people say they can notice changes as small as a third of a degree.
Assuming you are installing a longer aftermarket fork, a shallower head angle is not necessarily bad, and in fact might be good. But a decrease of half a degree or more should be justified. For instance, the new fork may be stiffer than the old fork. Or the new fork may have slightly more rake. More rake makes for quicker handling, which again will tend to cancel the slower handling caused by the shallower head angle.