PHP version matters or not?
A few considerations:

1) You want to be running a version that has security support. See https://secure.php.net/supported-versions.php  Both 5.6 &amp; 7.0 have support to Dec 2018.  Beyond that, you need 7.1+ (although 7.1 is not currently recommended for use with CiviCRM - https://docs.civicrm.org/sysadmin/en/latest/requirements/)

2) php 7 is faster than 5.6.  See http://www.zend.com/en/resources/php7_infographic  Why not run the faster version?

3) Maintaining support for old versions of php is a drain on development resources and prevents CiviCRM taking advantage of new php features.  

So, yes upgrade to 7.0 now (providing you are on the current 4.7.* release) and expect to keep upgrading.

[Edit: prompted by Graham's comment.]

Php requirements links:


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