It is important that you understand what an SSL Certificate is and how it works before deciding whether you need it or no. A simple Google search like "What is SSL Certificate" will educate you more on what it is, but for now, let's dirve in briefly on what it does and why you need it.
Once you have HTTPS enabled your website, browsers will show a padlock and secure message to your visitors. But more importantly, SSL helps in encrypting the communication between your visitors' browser and the webserver ensuring no eavesdropping or tapping of sensitive information by malicious tools or hackers when your users are interacting with your website over the network. Pause a bit and think, there is a series of communication that happens between browsers to web servers and most of it has third parties involved.
Simply put, SSL puts private communication between your visitors and the webserver. It is more like creating talking the browser will send gibberish that only your server will understand and none else. This is essential when dealing with things like logins (passwords), payments (credit cards), user details (identification), etc.
If you are not in need of SSL you can as well forget about it altogether and serve your website to visitors over classic HTTP. However, your website will not have the Padlock icon or the secure message on browsers and of recent Google Chrome browsers will even put a message 'Insecure' to your visitors when browsing your site. No harm shall come to your visitors without SSL unless they are entering sensitive information on your site. So a website that does not really have interaction with a user can acceptably ignore SSL.