How do you separate theory from reading within a person? Is someone who has no direction of play suffering from extreme form of tunnel vision and able to see only 4x4 grid at the time? Is someone who doesn't subscribe to "theory" reading out every variation of invasion against two point jump on third line before placing the second stone? All we know of a person's ability is how he fares in games against his peers. I don't think it's possible to dichotomize skill.

Summing up the thread, the consensus is reading is more important than reading, but better reading is better, and deeper reading is not better reading. Did I miss anything?

Normally westerners put a static emphasis on concepts that are really dynamic in Japanese (e.g. katachi/suji). This is a rare arsey-versey case. The Japanese term really means 'direction of groups' and the idea is that groups have directionality, or favoured directions in simpler English.

The value of recognising the favoured directions is that it can direct your reading. Humans cannot cope easily with the bushy trees that erupt when you try to read moves out exhaustively. Humans therefore rely on heuristics to prune the trees. The 'direction of play' concept is especially valuable because it allows you to prune the tree at a level much nearer the root than most heuristics.

Actually I find that amateurs have little difficulty in grasping the concept or in applying it in a rudimentary way. Their main difficulty is rather in realising just how far directionality extends. E.g. they tend not to realise that a group on the 4th line can have has a direct and strong impact on a group on the 17th line. Groups can have a slow, creeping, but still unstoppable momentum. If the cross-board movement of a ladder can be likened to an avalanche, other groups tend to behave like a glacier. Spotting the glacier's movement is ultimately what direction of play is all about, and so in some ways 'depth of (direction of) play is the concept to latch onto.

So you are saying the heuristics in "Direction of Play", allow you to read deeply(by pruning out variations), and there are other heuristics, that will also allow you to read deeply?

Of course there are. The (basic) idea here is that instead of reading out dozens of potential moves, the idea of 'direction of play' helps to limit ('prune', as John eloquently puts it) the number of moves to consider. It is much easier to read out four candidate moves than fourteen.

There are quite a few heuristics in Go that have been passed down which help in a similar way. The ideas of thickness, influence, moyo, aji, etc, can help us to think about where to start reading. Also, take proverbs such as 'don't play near thickness', 'there is death in the hane'... There are even proverbs and some shape knowledge which disposes of reading altogether. 'The bent-four in the corner is dead', 'play at the center of the bulky five'...

Speaking of shapes, a part of Go is about pattern recognition. Take tesuji exercises for example. You can read out a sequence, come to a point where you know a tesuji occurs, and it facilitates your reading in that regard. Or you can use tesuji knowledge to steer the flow of stones into positions that would allow you a tesuji. If your opponent relents, an advantage is often gained.

You've been learning all matter of heuristics to gain the upper hand, in many forms. These are just a few (rather scattered) examples.