I believe it would come in handy if we could do something like this:
fn main() -> Result<(), String>
if 1 == 3
println!("1 is equal to 3!");
println!("1 isn't equal to 3... (Well what do you expect?)");
Err(String::from("1 wasn't equal to three and you get punished."))
Clearly, there isn't any reason to waste space and typing on brackets on the first statement. It is already pretty straightforward.
Another advantage would be that this basically breaks no code. At the worst case, the compiler will implicitly insert brackets at compile time. Also I think it's known to everyone many C and C++ compilers support this.
Last, we could extend this to simply being indentation based (Like Python) and make brackets completely optional, but that's too crazy of a change for me so I won't elaborate further.