Adding a screwgate to the second knot is adding another single point of failure.
eg. if you lead on one rope, if you clip that to your harness, the rope or crab could fail. Whereas if you tie in (no crab), there's only the rope that can fail.
It's an almost trivial difference (especially with routine gear checks). It hopefully teaches you to tie figure-8's, and is a redundancy in case you're not savy with either system (which shouldn't be the case) |