Mike's right - the purpose of the TF Rubies is to automatically create mortises from the tenons you draw. Most scarf joints don't have M&T. But here's an example where the tenon has been split into two "joints", each cutting a thru-mortise in one blade of the scarf:
There are, however, circumstances where the tf rubies can help with non-M&T joints. In this key-lam example, each of the canted keys is actually a pair of "joints' that cut the triangular shaped notch in one of the beams. So if you move the keys around, the notches will follow:
