I am only dabbling in gardening, so to speak. I am still trying to figure out the growing season and climate here in WYoming at 7500 feet. Went from northern Wis. with 36" of rain to the high mountain desert with 12" of rain per year.
My biggest problems here are soil and animals. The soil here has no organics in it. It is rocky and drains away water like a sieve. If it weren't for the raised beds and homemade soil mix, I wouldn't have anything growing. We have tried to start a lawn twice now, and just can't get the grass to grow. Barely even have weeds growing, the wind blows all the fines away and all we end up with is a layer of rotten granite chuncks. So the raised beds excel for that aspect.
As for animals - if it is green, they will eat it. Gophers, ground squirrels, rabbits and antelope. If you don't protect the plant from the wildlife, it will get eaten! My poor irises have been eaten to the ground more than once this summer. They get about 6" tall, and then they are eaten down. The raised beds make it easy for me to wire under underneath the beds to keep out the diggers, and wire over top to keep out the grazers. Having the plants concentrated to a smaller area makes this fencing economical.
Last year with 6 tomato plants in my little 3' x 7' growhouse, I grew enough tomatoes to eat, to share with two neighbors, and to dehydrate some for crunchy salad toppers. Probably about 1 bushel total. Granted, I put them out about a month late (June), but they were still covered in green tomatos and producing more in November when they finally froze and died.
This year I have lettuce coming out of my ears. I have been giving away about a 1 gallon bag of lettuce each week and eating about the same amount. My peas are producing a second crop, I think I will have gotten about an ice cream bucket full by the end of the season, and that is for only 4 square feet of space.
Advantages of square foot gardening for me: smaller foot print (for animal control and drip irrigation) and ability to create a growing medium.
If you create enough bed space, I believe that you could grow as much garden crop as you want. It is more intensive in some ways - continually monitoring for insect and disease infeatations. With the way the plants are packed closely together, I can see where these issues would really be a problem if they set in. I use drip irrigation, so I never have moisture on the leaves. It puts the water where it is needed right at the plant so I can conserve water. And I believe this also helps with weed control.