<p>The packages included in Tails are carefully tested for security. Installing additional packages might break the security built in Tails. For example, installing OpenVPN might modify the firewall rules that Tails uses to force network traffic to go through Tor. So, be careful with what you install.</p>
Some software might, for example, modify the firewall and break the security built in Tails. But other software like games or office tools are probably fine.