The decap die is intended to clear the primer as a precursor to brass cleaning.
As BigEdP51 points out, the risk is with brass that hits the ground in a dirty place that makes a mess of your other tools and dies. If you want clean primer pockets, or very sterile necks prior to annealing, it is common to wet tumble with the primers removed in advance.
Depriming prior to vibe tumbling isn't really necessary as compared to wet tumbling with stainless pins. So the need to deprime prior to brass cleaning is really a matter of your overall process needs. Using a universal decap die is also an option since there are hand tools that do this task as well.
If I mount a case kicker on the RockChucker, I can run the deprime operation quickly. If I am decapping brass that may contain crimped primers, this is less wear on my fingers since that takes a fair squeeze with the hand tools when you run into a crimped primer. So for me, having the option to decap on the press when I know there will be crimped primers in the mix is one good reason the dedicated universal decap die serves a common purpose. Crimped primers come up in the context of short line service rifle brass in 223, 308, and .30-06 mil-surp.
You don't have to wet tumble, and you don't have to use crimped brass. When these things come up, the universal decapping die is a good option.