After you have installed Kali Linux, it is not a bad idea to update the distribution to ensure you have the latest version of all the tools and to apply any patches and other fixes that may have been released. You should not only engage in applying updates to a system after you install it, but you should also do it on a regular basis for the same reasons. The reality is that updates and patches are released fairly regularly, so it is best to make it a habit of checking for these, so you don't miss anything or leave yourself insecure.
It is important to recognize that an update should always be run immediately after installation is completed as well as on a regular basis. This is for a number of reasons, mainly that new tools can get released or new updates to application databases may have been made since the image or ISO file have been posted on the website. Not to mention the fact that updating software regularly is a key factor in protecting yourself from security issues and concerns as they arise.