Velocity restriction/scaling/mapping when generating a drum kit from a loop or longer sample can be extremely useful for sample selection, round robin style, etc. For example when the first loop is sliced it can be restricted to velocities 01-0f(skip 00), second loop can be 10-1e, third 1f-2d,etc. It is useful because once the velocity is modulated or scaled, it chooses a new sample. Any velocity modulation plugin or script could in turn create round robin sampling or other useful sample selection tools. It could also be used for duplex devices that set input step velocities like the launchpad step sequencer. The velocity bar on the right could be 8 possible loop slices for C-4.
And true it could be said to just use a pitch mod or arp to mod the current system, and change slices that way. But it is my perspective and experience it is easier to deal with velocity data changes versus pitch data changes.