Joomla 3.6.3 was released on October 18, 2016. It's a bug fix, so if you want to do this update, you can but it's entirely optional.
Joomla! 3.6.3 Released (joomla.org)
Joomla! 3.6.3 is now available. This is a bug fix release for the 3.x series of Joomla. This release fixes a Backwards Compatibility Break we made in 3.6.2 with the article ordering. In addition there are a large number of minor improvements and bug fixes.
TYPE OF UPGRADE: Bug
MAJOR OR MINOR: Minor
SUGGESTED ACTION: You can wait.
WHY: To fix some bugs in the software.
Here is more information about how Joomla classifies their upgrades.
Our Website Maintenance Department will be in contact with all of our clients running Joomla regarding these upgrades and we'll get you a quote.