So the idea behind square foot gardening is to minimize the space needed but still grow the same amount of food as a traditional row garden. Mel talks in detail in his book about what a waste it is to plant a whole row of seeds, and then thin the seedlings down until the plants are, say, 4 inches apart. By planting in a square instead, in a specific formation, one could have 8 plants in a two-square-foot area and still have all 8 plants spaced 4 inches apart. This would take two linear feet of space in a row garden, plus at least two feet of walking space on either side of the row, resulting in 10 square feet of space to plant the same amount of plants. Even dividing the space allotted for walking between the two rows that would line it, requires 6 square feet of space for the same amount of plants. By eliminating the need for walking space, one can effectively eliminate 60% or more of the space needed for growing. How awesome is that?!The “Mel’s Mix” that SFGers are always talking about is composed of 1/3 peat moss, 1/3 vermiculite and 1/3 a compost blend, made of at least five different compost sources. Creating this mix for use is raised beds also eliminates the problems many of us face with poor-quality native soil. Additionally, if you construct and fill the raised beds in late winter or early spring, you can begin planting earlier in the season because your new Mel’s Mix is warmer than the ground soil.
This is obviously a very "quick and dirty" rundown of square foot gardening, but these are the points that sold me on the process. If you haven't looked into it for yourself yet, I hope you do!