HTTPS has always been used to secure websites that contain sensitive information such as Credit Card numbers, but most web site owners tend not to give it much thought outside those requirements.
In 2014 Google announced it was starting to give a slight ranking advantage to HTTPS sites over their HTTP counterparts. This started out as being pretty much a tie-breaker scenario, where two sites were otherwise equal it would rank the HTTPS site first.
Last year Google also started actively looking for HTTPS content ahead of HTTP content. That means if your site supports both protocols Google will automatically look for the HTTPS version.
With the advent of HTTP/2 and it’s current requirement of HTTPS now is a good time to consider switching over to HTTPS. As well as giving your users a more secure experience you also have the added benefit of being in a good place to support HTTP/s if your host supports it.