The Cow Cavalry used cattle whips to encourage the animals along. That was their primary function. However, I imagine that the men of Munnerlyn's Battalion also used their whips for another practical task: sweeping those obnoxious spiders out of the way. I mean, unless they really enjoyed riding through spider-webs and getting spiders on their hats, in their faces or any other place a spider might wind up if you ride (or walk) through their web.
I don't think that observation will probably end up in the documentary, so this is an exclusive, inside piece of info ; )