Why only till the top three inches? Because it's rocky below that. Every time I till, the tiller kicks out a few more rocks. So over time, the bed gradually gets derocked. Rather than spend all my time digging rocks I'd rather get things growing. Rock removal can get done bit by bit as the years go by. By the way, I only remove rocks bigger than a hen's egg. The smaller rocks stay in the garden. Rocks provide minerals and improve the structure of my soil. As long as my little tiller can deal with the rock, it stays.
So I've just added 300 sq ft of garden beds. What to plant? Peas and some more beans. I'm going with a couple rows of snap peas, a couple of snow peas, then what space is left will be divided between a purple bush bean and a yellow one. Just adding some variety.
For the record.....
72 sq ft ---- peas
228 sq ft --- beans