Nulled files often contain hidden malware, backdoors, or malicious code . Hackers use these to gain access to your server, steal user data, or use your site for spam and botnets.
You will not receive official security patches or new feature updates. If the script breaks during a PHP or server update, you will have no access to developer support to fix it.
Most developers provide a free demo of their script so you can test all features before spending any money.