In all the time The Golden Trio spent fighting Lord Voldemort, why did nobody ever go to the Room of Requirement (once they had discovered it), and say "I need a way to defeat Lord Voldemort permanently"?
Am I the only one to find it suspiciously convenient that Hermione, who was the much-vaunted "Brightest Witch Of Her Age", never once suggested they make use of the Room Of Requirement to learn everything they possibly could about either defeating Lord Voldemort for good, or at the very least learning everything there was to know about Horcruxes and how to destroy them?
If you read the series, you find out that the specific books pertaining to Horcruxes which initially resided within the school library's Restricted Section were removed by Dumbledore around the time Tom Riddle started asking pointed questions about the Horcrux process. Those books remained in Dumbledore's office until Hermione summoned them in Book 6 after his death (which raises another question about warding which I won't get into here).
If the Room had so much potential, and was capable of providing a fully-functional DADA training facility, why not a library to research either a way to defeat the Dark Lord, a way to destroy Horcruxes, or both?
For that matter, if Tom Riddle knew about the Room of Requirement, why not side-step Dumbledore's attempts at blocking him by asking the Room for everything he needed to know about Horcruxes?
And after the all the Time Turners were destroyed during the Big Fight in the Ministry of Magic, why didn't anybody go to the Room of Requirement later on and ask for a room full of them?
It seems to me that this Magic Room probably has infinite (or very nearly) potential powered by the very magic of the Castle itself, and is at least semi-sentient in order to understand, and process requests then produce the expected results, and yet, was probably the most under-used asset available to Harry.
Let's be honest here! If you were in Harry's place, and you knew (as he did before he left the school at the end of Book 6) what you needed to do, wouldn't you go to the Room of Requirement and ask for a room full of Time Turners and books with everything there is to know about finding and destroying Horcruxes?
Bottom Line (or TLDR): Is there a clear reason given for why the Room of Requirement (which doesn't appear to have any limitations) was so under-used?