Some network guys I know prefer fibre even within the rack, just because they don't want the weight and the obstructions in the rack. Apparently more than once the weight of the DACs and the bulk of the cable bundle has caused a problem with NICs.

Personally that surprised me, but I can see where they're coming from.

Yep, I did this for my little DGx spark cluster because 100-200gb copper cables are very thick, heavy, and annoying.