The post you’re replying to is saying they went FROM always having the component mounted (at least in the component tree if not in the DOM as display:hidden), TO only mounting the component when it needs to be open. They moved from the way you’re talking about, to creating the component/DOM nodes only when needed.
Excessive nodes - hidden or not - cost memory. On midrange Android it’s scarce and even if you’re not pushing against overall device memory limit, the system is more likely to kill your tab in the background if you’ve got a lot going on.