I'd love to learn a bit more about this technique and its context of use, as it's not something I've encountered elsewhere yet. My current assumptions from Chris' descriptions are that this is used when fitting a tenon shoulder, where the flush cut saw is able to use the mortise shoulder as a reference plane. Does that cover it, or have I missed something?
Some questions on my mind:
1) All (again, western) mortise-and-tenon joinery discussion I've seen to-date has focused on using either a shoulder plane or a chisel to adjust tenon shoulders. Where does kerfing fit in the range of fitting techniques? The opportunity to use the mortise shoulder as a reference plane seems pretty powerful.
2) Are there situations where kerfing is particularly appropriate, or inappropriate?
(**) My curiosity piqued, I dug around for going prices Yataiki saws. This expression resulted:
![Shocked :shock:](./images/smilies/icon_eek.gif)