A lot of writing code on the Internet Computer deals with numbers that have n digits – ICP e8s, a trillion cycles, etc.
Instead of typing out 100_000_000 or 1_000_000_000_000 adding something similar to the 1e8/1e12 TypeScript language syntax, but for Motoko would make the code a lot easier to review and and less error prone. Including for when AI starts creating DeFi apps that handle money 
Yes there’s Nat.pow(10, 3), but that requires a computation so these can’t be constants at the top level of actors.