Not speaking to their implementation, but prefix sums/scans are simply a very useful primitive tool for parallelizing many otherwise sequential operations. For

Not speaking to their implementation, but prefix sums/scans are simply a very useful primitive tool for parallelizing many otherwise sequential operations. For instance, appending a variable number of items per worker to a shared coalesced buffer uses an exclusive prefix sum. This is probably the most common use case for them in practical programming. They can also be used to partition work across parallel workers (segmented prefix scans). In lieu of pointer chasing, hashing and the like, parallel operations on flat arrays are the way to maximize GPU utilization.