Of all the training I received in the RAAF, I believe the decompression chamber is/has been one of the most useful. Each and every person has their own symptoms and until you experience it you will never know what yours are.
Yes, you can read about the potential symptoms in a book but after every chamber run the variety of symptoms amongst the victims was all varied and very few exactly like the book.
I know it's all about dollars these days but it would be handy if every ATPL (or CPL) had to go through it once.