All new websites set up are now defaulting to PHP 7.0. Apart from being a more recent PHP release with several new features, PHP 7 is considerably faster than its predecessor (PHP 5.6 – there was no PHP 6). That is to say, your website will load faster!
We are not at this time changing existing sites to use PHP 7.0, as it does have more backwards incompatible changes than usual. As such, existing websites need more individual attention to make sure that they will have no problems. Any complex code written more than a couple of years ago is more likely to include constructions which are not supported on PHP 7.0. So, for example, you may wish to check if you have any plugins on your WordPress site which have not been supported by their authors for a long time and need replacing with something more up-to-date. It’s worth doing – as you can see in the previous link, PHP 7 is not just a little bit faster, but much faster.