:refer :all

I'm just getting started with Clojure, so this is more a question than a recommendation.

In the `:require` portion of each of the files it has a `:refer :all`, like this:

``` clojure
(ns koans.01-equalities
(:require [koan-engine.core :refer :all]))
```

I'm using Calva, and it surfaced this warning:
`use alias or :refer clj-kondo(refer-all)`

Should the code referenced above be changed to the following?

``` clojure
(ns koans.01-equalities
(:require [koan-engine.core :refer]))
```

What is the significance of including or omitting the `:all`?