Obviously, the slash at the end is not needed in order for the URL to work, but it would be considered to be proper style. The short answer: it’s faster for your server – additionally when the end-user (browser, search engine) receives a faster response from the web server, generally everyone is better off.
A more detailed answer if you are bored:
Just like your computers file system, URLs are hierarchical in structure.
yourdomain.com/casinos/reviews/
The very first thing that’s done to resolve the URL is that the base directory is located – everything after the right of the final / is ignored. Looking to the right of the final slash gives us the final segment of the URL, the document being requested. A slash at the end tells us that the final segmant is null, and to look no further. When no slash is used, the final segment cannot be assumed by the server, and in most cases the web server sends a redirect message, then the browser requests the correct page to display.
So basically, as you already know these redirection errors take place behind the scene, and URLs without a final forward slash will still load. However, this can waste time and resources. Considering the massive amount of users and content on the internet, this could amount to a lot of wasted time…
Additionally, the browser automatically assumes that with just a hostname request you want the main index to display. This means that hostnames with final slashes are only in good form.