I found myself asking the same question. 64 bit integers are useful because you'll never fill up an IntMap with a uint64 key, and 256 bit integers are useful be

I found myself asking the same question. 64 bit integers are useful because you'll never fill up an IntMap with a uint64 key, and 256 bit integers are useful because they offer sufficient (128 bit) collision resistance. In my mind, a uint128 is too big for use as an index, and too small as a GUID.