depending on the area of the country that you live putting rigid insulation around the foundation wall is a great idea. the only thing is if they are only excavating a small area of your foundation wall you will only insulate that small area. unfortunately i dont think that you will see much benfit unless the entire bsmt wall is done or at least all walls in a single room or area of your bsmt.
Thanks! They're doing the whole front of the house, which is also nearly everything that's below grade. I'm planning on heating the basement, so I figure putting a thermal break between the concrete block and the earth would help. I'm thinking of like R4 or something.