[richardknop]

Sanitization does not refer to escaping HTML entities before rendering to avoid cross site scripting. That is just escaping of entities done when rendering templates.

I believe by sanitization most people mean processing content which will be rendered and not escaped, a good example is content from WYSIWYG editors. And this is where sanitization libraries would come into play.

You would sanitize HTML fragments before storing them in database because you don't escape them during rendering. Text content is not sanitized before saving to database as you can just escape it when rendering.