Well, if you add a semi-colon where it's not supposed to be you'll get a compile error. If you omit a semi-colon, you'll also get a compile error. They're just there to separate statements (Rust is not whitespace-sensitive).

The most common pattern in my Rust code is:

`statement; statement; expression` where the expression is what I actually want to return from this function

it seems more noisy to say `statement; statement; return expression;`