If you are using server side rendering for SEO then it makes a difference. If you have not mounted the component, google will not see it to index its content. If you on the other hand are using display: none, google will be able to see it's content even though the user don't see it.
One usecase where you want google to index non visible content could be an e commerce site which shows product information inside tabs. You wan't google to index all the product information, not only the content available on page load.