I don't know Zig, but conceptually: a direct pointer is the fastest way to access an object. An arraylist is the fastest dynamic sequence of objects (fattest in access, not in growth). You use these when you need the performance. It's not often but it certainly happens. The most trivial example is a string that you append to but still need to pass to a C API in between that expects it to be contagious, but it's far more useful than just for storing characters.

Sure, in cases where you need elements to be contiguous in memory then certainly an unrolled linked list is not appropriate. There's usually not a meaningful performance difference between a pointer deref and an indexed array access, however.