In reply to:

So how does one know if these things are needed anyway?



It's a very good question and I don't know an answer.

On the one hand people are very obsessed with the flatness of the amp and speaker frequency curves. On the other hand, an untreated room can introduce very wild +/- 10 db peaks and nulls.

The wisdom is that treatment helps but to what extend and at the expense of what damage to the wallet and to the room aesthetics - I don't know.