template security

I can select this options in the templates for the addons I created: There are no more details. So I wonder what effects are when I enable this. In what cases should/may you enable this option?

Enhance the security on your site using this very basic add-on. There has been a surprising increase in malicious attacks to XenForo sites through injection of malicious code into your templates. Limiting the access of all templates to yourself and a small handful may not always be a...