Actually the size of indices can be important in real life. For example, on Nvidia GPUs, a kernel that indexes data with 64-bit indices will usually be much slo

Actually the size of indices can be important in real life. For example, on Nvidia GPUs, a kernel that indexes data with 64-bit indices will usually be much slower than one that uses 32-bit indices. (Hard to argue that this is related to big-O since there are only two data points, but I'm just pointing out that index size is in fact a real-world concern).