As Russ mentioned, the accuracy of the method is dead on. However like any direction finding, it requires skill to keep headed in the right direction, especially in unfamiliar, featureless or dense terrain. Some people will initially get themselves headed in the right direction but will soon deviate as they start off with the sun on one shoulder, to their back, or their front. It might not occur to them that the sun is still moving through the sky but they keep with the original thought that N/S/E/W "must be that way" because that is where the sun was on their body when they stopped to find their initial direction.

Even in as a little as 1/2 hour, you can be degrees away from your original, targeted direction enough to miss that crucial trail junction, trailhead, water stream etc.

This same principle applies to using a compass. For example; if you look orient your compass to North then deviate 5 -10 degrees away from North, it does not look like much at a short distance, however over a much longer distance, you can be far enough off direction from your destination that you may not notice and miss that trail junction etc by a fair amount if you do not take the time to take compass readings as you go.