One of the Roubo components I was most weary of before I built one was the crochet. One would think the leg vise would be enough to anchor long horizontal pieces when planing edges. Would an installed crochet stick out too much and get in the way?
During the design phase, I went for a removable crochet. Unlike the large traditional crochet (e.g. this one shown in a video by Steve Branam), I had opted for a simple dowel that slots into a hole just in front of the planing stop. Maybe this is not technically a crochet as it does not hook around the work, but more of a horizontal planing-stop.
Looking back, I now see the inclusion of the stop as an almost critical element of the bench. Many times, the clamping power of the vise alone is not adequate to prevent movement of a large piece during planing.
The main advantage of a traditional crochet, however, is that work can be wedged into it so there is less need for a leg vise at all.