Recently Google moved entirely to secure search which will force the clients to use HTTPS instead of HTTP. Google safe search policy depends on the adding/manipulating the search url with is only possible if ProxySG is having visibility to the full url. In the case of HTTP, this is not a problem as the url is in clear text always. When HTTPS is coming into picture, the full url visibility/manipulation option is only available when SSL Interception is turned ON.
For those customers who are not using SSL Interception for Google domain, policy enforcement of safe search will not work.
Some more information on Google Safe Search https://support.google.com/websearch/answer/186669?hl=en