Oh, I just read the rust doc and its says "once a value is bound to a name, you can’t change that value." but I've thought of immutability the other way around, once a name has a value, it can't be changed.

I thought the value of const was once you read const x = 1024, you can be sure that x is 1024 while its in scope, that subsequent code can make assumptions about the content of variable x. Or, when you see x in the code, you can jump directly to its definition and know what its value will be. Defined once and not changed.

Apparently I don't understand the value of const at all.