Over at The Classical Budoka, there was an excellent post on the importance of studying distance in martial arts. Below is an excerpt. The whole article may be read here.
44. Ma: Fluid Space in Budo
December 12, 2011
In budo, like other physical endeavors, the interconnected factors of space and time (rhythm and timing) are crucial. In Japanese, the term for “space,” in between objects and opponents is “
ma,” and the character can also be pronounced “
aida,” as in “in between.” It is the space “in between” yourself and your opponent, the empty field that defines the potential of attack and defense, the
ma-ai(the “meeting” space). Like music, however, “empty space” between notes or opponents aren’t “empty” in a sense that there’s nothing there. Potential is there. Fullness is there. Emptiness is necessary for fullness. Spaces between individual notes creates a song, its tension and melody. Space between adversaries define the field in which they fight, and the person who can control the space (and time) best is the one who wins.
An understanding of ma-ai (the proper distancing) is important, but many martial artists of even respectively high levels in their specific art aren’t aware of it beyond their particular specializations. Worse,
kata-based training (especially when done individually, such as in karate kata and iaido) may make a person ignorant of proper ma-ai.
...
There’s an article that Diane Skoss, of Koryu Books, wrote about being a woman training in koryu budo. She made a comment that, even after years of aikido, she never understood mai-ai very well until she started weapons work in koryu. Then all of a sudden, she had to deal with opponents who came at her with short staffs, long staffs, naginata, spears, swords and all sorts of weapons, long and short.
Such training gave her an innate understanding of the elastic, variable nature of ma-ai, dependant on the situation, attacker, angle and weapon.
That is why, I suspect, that Okinawan karate and aikido included some kind of weapons training in their curriculum. Even Kodokan Judo had weapons work, but discarded them as it evolved into more of a specialized sport, and less of a martial system. If you don’t get out of your comfort zone in ma-ai, you won’t understand proper distancing. So this is an argument, in a way, for studying weapons if you are primarily a grappler or puncher-kicker.
In classical systems, there are various terms to explain ma-ai. The most common are the three different terms of
toh-ma, uchi-ma, and
chika-ma to denote the three basic distances. Depending on the weapons (or lack thereof), toh-ma is when the distance is too far (toh- is from the word for “far away,”
toh-i) for you or the opponent to strike, unless you take steps to close the gap. Although you can begin to engage the enemy at that distance, you won’t be struck easily.
...
The problem with ma-ai is that there are so many variables. Not just in terms of weaponry, but also in terms of rhythm and timing, angles of attack and positioning of the attacker and you. All of these will affect proper ma-ai. Space and time are not separate entities. They interact with each other.
While we’ve been discussing the physical tactics of handling space, we can’t also forget the mental/psychological and psychic overlay of spacing. In esoteric doctrines in some sword schools, even standing at a distance, you have a kind of mental uchi-ma; i.e., you can still be too far for a quick strike with your sword, but if your spirit and energy is strong enough, you can already attack the opponent.
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. The first book is 
(by Sun Tzu's great-grandson) is a brilliant elaboration on his ancestor's work. 
