What's your opinion on using "let ref" to create references?

let hello = &s[0..5];

let hello = &mut s[0..5];

let ref hello = s[0..5];

let ref mut hello = s[0..5];

I really like "let ref" to create references. To me, it sounds better. But nobody uses it.

What do you prefer? If not "let ref", why not?