I was just reading the Swords & Wizardry forums and found a thread about how neat it is to be able to take the .doc format file of White Box edition and edit it to the rule hack you want. The reason it is so handy, according to one poster, is that you can make a booklet with just the rules for the players. Even though it's not always explicitly said, that do imply that there are rules just meant for the game master.
When I was younger, and was first introduced to this wonderful hobby of ours, everyone read all the rules. One boxed set with one or two booklets was the norm. But, in contrast with, say, D&D it wasn't clearly labelled for the Player and for the GM. I haven't asked anybody else about it, but I think most people did like we did, and bought the box if you played the game. That usually meant that in each group you had maybe half as many copies of the rules as there were players. It also meant that almost everyone had read everything in there, including the rules for casting and learning spells, the chance to catch gangrene or what modifier you'd get for trying to use your Listen skill in thick fog. I never saw a problem with that.
When I first actually opened a rule book for D&D, it was the 2nd ed era. Not only were there two books, they also had the weirdest layout with the same section in the two books saying slightly different and (in theory) complementary things. I was thoroughly confused. For some reason there were things which you got the impression you should hide from the players! With my background that seemed preposterous. What was there to hide?!
Now today I realized that this way of splitting up information have shaped me more than I've imagined. The idea of having a standard list of magic items which sooner or later everyone knew about, or a list of standard monsters, is just an alien concept where I'm coming from. Now, many years later I have kind of adapted and know that the way things are, can be different in different places. But, to put this in perspective I think a game were everyone knows how to play the game, but where magic and monsters are all unique creations by your GM/DM is really a more interesting way to play the game. The mystery and wonder of fantasy sure is easier to maintain that way, and for those interesting in the history of the hobby it is the way to experience how it was when Ken and the Phoenix circle, Dave and the Twin Cities players, and Gary with his Lake Geneva group played. Nothing was yet codified, and every piece of magic was new, and wonderful. Imagine that.