Just wanted to add that while I think it's slightly better to do all the ditch work first & then go back and FMQ, I have seen award-winning quilters who would SITD entirely around one block & then fill that block in, and repeat all the way out to the edge.
Also, I don't think anyone's mentioned yet that one benefit of SITD -- even if just with wash-away thread -- is that the seams don't puff up slightly like a little mini hill. Sometimes for family quilts, I don't mind the hills; they're not very obvious -- esp. to non-quilters & there are only so many hours in the day, but it definitely looks nicer to SITD first.