The main operation I can think of is multiplying by a ratio without losing precision. If all your values are specified in 64-bit fixed point, a 128-bit integer

The main operation I can think of is multiplying by a ratio without losing precision. If all your values are specified in 64-bit fixed point, a 128-bit integer type gives you something with enough bits for the intermediate product. It's not something I've really dealt with myself, but I seem to remember reading that this is really handy to have in some physics simulations and control system algorithms that do numerical integration. At any rate, it's important enough that many Forth dialects have a word for this specific operation [1]. [1] https://www.forth.com/starting-forth/5-fixed-point-arithmetic/#Star-slash_the_Scalar https://www.forth.com/starting-forth/5-fixed-point-arithmeti...