Deactivating plugins in WordPress does not usually impact site speed because they are not loaded or executed. This can be beneficial for troubleshooting or testing new configurations without permanently affecting your site's performance. However, it's essential to be aware that deactivated plugins still occupy space in your database and file system, which may lead to increased storage usage over time. More importantly, deactivated plugins can pose potential security risks if not regularly updated. Outdated plugins may have known vulnerabilities that hackers could exploit, leaving your site susceptible to attacks. To maintain a secure and efficient WordPress site, it's crucial to periodically remove unnecessary plugins, update active ones regularly, and delete deactivated plugins to ensure the best possible performance and protection against potential security threats.