What are the advantages and disadvantages of using parentheses for the condition of an if statement?

Question

I am writing a simple programming language. I see some programming languages use parentheses for the condition of an if statement but some do not.

What are the advantages and disadvantages of using parentheses for the condition of an if statement?

For example, in Rust, the if statement looks like:

if number < 5 {
    println!("condition was true");
}

Answer 1

What would this mean?

 if a b

You can make this easier to parse and/or to comprehend by several methods:

 if (a) b

 if a { b }

 if a then b

but you probably can't leave it as if a b. The choice is a matter of taste and consistency with the rest of your programming language.