The general philosophy of SMaSH is to simplify a recipe down to one malt and one hop to get a good picture of the flavor contributions of each. While technically most extracts aren't made from a single malt (a few are - Northern Brewer's Marris Otter extract is one.), you can still get a good picture of how that single extract type works with a single hop variety. If you are an extract brewer, this can be just as useful of a tool as a true SMaSH beer is to an all-grain brewer.