SSL encrypts the communication between the visitor and the website. Any traffic intercepted between these two endpoints is unreadable. This is key for any ecommerce site or webshop that is processing or acquiring personal or payment related data.
Websites with a valid SSL certificate are now preferred by Google, meaning whether your site has an SSL certificate or not will affect the website ranking within the search index, which of course will affect visitor numbers.
Sites without SSL are now marked as not secured by Chrome i.e. Google – this can often alarm and concern website visitors that their data is not safe. It even look bad for information only websites such as blogs, where an SSL would not be necessary as many users don’t really understand the warnings or what SSL is. So in essence it is advisable for any website to use SSL.