Basically I wanted a pleasing way of joining granny squares that would mean I wouldn't get the clusters touching each other when I stitched the squares together like most joins do. I wanted to continue the alternating "gappiness" throughout (if that makes any sense at all!). I also wanted to join my granny squares with crochet rather than stitching as I wanted it to be stretchy throughout, but I didn't want raised slip stitches.
The above link was exactly what I was looking for.
The pics aren't as polished as other crochet blogs but the instructions were good and once I got going it's fairly intuitive.