While you wouldn't want to leave "console.log" in your code in production, you can use them in function components just like a classes' render methods.
A better example (from the video "React Today and Tomorrow and 90% Cleaner React With Hooks" from October[1]) is something along the lines of updating document.title = `${some} Page` or possibly calling an API.
The console.log was only there to illustrate that the code in useEffect's callback is only being run on the client-side (see the codesandbox I linked to).
I think it's clear from the parent I was responding to that they have better use-cases in mind :)
The 'useEffect' hook - it won't be executed if you use e.g. ReactDOMServer.renderToString() for SSR
Codesandbox: https://codesandbox.io/s/peaceful-dew-nvw83