Alright, so it can only prebuffer one thing, or have one copy of the video bufferred or ready to go any any one time. 😞 It probably makes sense to have it prebuffer preroll ads, as those aren't generally paused, resumed, or seeked to a position - they are short form content with a single playback choice. If you prebuffer 'resume' or a chapter button and the user selects play from beginning or a different option then that bandwidth is wasted, so this doesn't change anything or invalidate the other problems.
Also if you only have one choice on the screen then prebuffer would be doing its job. If those links are the only 'solutions' then those are the only situations a production environment would be using this feature IMO.