I have mixed feelings about a crotch strap and I am not as "sold on it" as others. I recently (late October / early November) did a trip on the Aquacat LOB in the Bahamas. This was my first trip using a BP/W set-up. The water temps were warm enough that I dove in a swim suit, rash guard & 3mm vest. After a week of diving in a swimsuit with a crotch strap, it was chafing pretty significantly. The webbing on the crotch strap was much more flexible than that on my harness, but it still was not comfortable by about mid-week.
I realize that this would likely not have been an issue at all if I was in a wetsuit, and it is very definitely what some might call a "First World Problem", but it was enough that it made me consider diving without it.