<p>The packages included in Tails are carefully tested for security. Installing additional packages might break the security built into Tails. For example, installing OpenVPN might modify the firewall rules that Tails uses to force network traffic to go through Tor.</p>
Some software might, for example, modify the firewall and break the security built into Tails. But other software like games or office tools are probably fine.
If you choose **Install Only Once**, the package is also saved in the Persistent Storage but won't be reinstalled automatically every time you start Tails.