A lot of chi sao is redundant in actual fighting.
Chi sao gives us many attributes but we need to literally " step away " in different directions so the facing and arm skills are used when engaging a " moving target " capable of erratic movement ... Not just ygkym and rolling arm combat.
Certain arm angles are developed for maintaining their integrity when making sudden impact. Bong sao is "developed" in chi sao along with other drills but the redundant factor is a bong doesn't have to seek contact to be created. It can be as chum kil , a combination of dynamics involving timing to harness forces capable of creating opportunities to lat sao jik chun. Whole body lsjc.