Intellij needs permissions so that it can for instance seamlessly download plugin you chose, or maybe if your build setup is configured for different artifactory to get it's code snapshots from (for example when you include package in your pom - intellij in the background when you press maven refresh downloads that from maven repo to your local .m2 folder. To install git when you first time installing Intellij on the system and git is not found on path. If you have 'Code With Me' plugin in Intellij so that it can function properly, and so many other stuff.

Usage statistics is different setting - related to firewall settings but not only thing that goes through firewall, and btw you can disable it.