In order to reap all the benefits of SSL you must have end-to-end security
One of the most common mistakes with regard to SSL Certificates is that companies purchase one, but then only serve their website over HTTPS on login and check-out pages. This is a problem as it prevents websites from leveraging all the benefits that an SSL Certificate has to offer.
There are a few reasons you, as a website owner, should encrypt your entire site–not just the pages you think need it. For starters, Always-On SSL, as it's called, is widely considered a best practice by organizations like the Online Trust Alliance. It helps protect against attacks like sidejacking, as well as hacking through threats such as Firesheep and malicious code injection.
Beyond that, the internet is moving towards a fully encrypted model. The browser community is about to begin warning web users when they attempt to access sites that are not encrypted. This means any page on your site that is not secured will prompt a browser message that indicates to the internet user that they are about to go somewhere that is not secure. This, for obvious reasons, will dissuade many users and could end up hurting your traffic and possibly your business.
In addition to this, HTTP/2, the eventual successor to HTTP, is becoming adopted more widely across the internet. HTTP/2 requires an encrypted connection to work. This means your site will need to have Always-On SSL, not just a few key pages with encryption.
And finally, Google announced in 2014 that it would start to use SSL Encryption as a ranking signal, meaning that if your site is encrypted it will rank higher than other non-encrypted sites. This is great news for your website, but it's only possibly to achieve the rankings boost if you're practicing Always-On SSL.
A single certificate can secure every page on your site. It's just a matter of configuring your server the right way. So with that in mind there's no reason not to serve your entire website on HTTPS. You've already purchased the SSL Certificate, you know it's a best practice and the only way to leverage all of the benefits of the SSL Certificate. So go the extra step–enable Always-On SSL.