Interesting. But I think what you're saying is that many pilots feel
uncomfortable lowering the wing enough to fully align the gear with
their ground track, so when they land, they still need to skid the
fuselage around. I suppose this makes the flare a little less dramatic,
and therefore less error prone. And keeps the lowered wing a
comfortable distance above the ground. My quibble then is only with how
you describe. I don't think you combine a side slip with a crab: this
gets back to that implication that they are somehow additive. Instead,
you are combining a side slip with a pretouchdown skid. The primary
advantage is that you get a more wholesom view of the runway on final.
The disadvantage is that you have less yaw authority to swing the
glider during the flair. (Remember the ailerons have some effect as
well. You can increase the rate of yaw significantly with crossed
controls: kicking down wind while lowering the upwind wing as you
flare.)