“Rapid Security Responses are a new type of software release for iPhone, iPad and Mac. They deliver important security improvements between software updates – for example, improvements to the Safari web browser, the WebKit framework stack or other critical system libraries. They may also be used to mitigate some security issues more quickly, such as issues that may have been exploited or reported to exist.” — Rapid Security Responses
This is new, at least for me, and interesting. There seems to be more to gain than to lose by installing, and enabling it. Done!