I have not seen many projects joined this way - but it is one of my favourite joining methods, especially for granny squares where it just adds that something extra.
One of my lovely FB friends pointed out an example of something similar, where the squares are joined on the back by single crocheting through both sets of loops across every stitch. So in other words the Single Crochet Join (but instead of working on the front of your squares you work it on the back to get a reversed effect).
Working the single crochet join invariably gives you a ridge effect - quite a nice effect for projects such as bags where a bit of "puckering" is not problem. However, a blanket that puckers would drive me insane!
Working it the way I do reduces the ridge effect substantially and your work should lay flat.
To cross over into the next set of squares 2ch, then insert hook through corner of both and continue as explained above.
A FEW NOTES:
I always use a hook 0.50mm larger than the hook I used to make my squares.
Try not to hook too tightly
When joining over granny clusters ch 3 and sc into the space between the clusters