There are many who view precious metals/commodities from the standpoint of being nothing more than a high risk gamble. For most who are "investing" in them, that is exactly what they are, a high risk gamble...putting their money in them specifically to see the value increase.
However, the theory behind having precious metals and commodities in a portfolio is as a hedge/protection, not only in the event that markets collapse, but should we have an economic/financial Armageddon. It's less of a matter for expecting the value to go up (which it likely would during a collapse), but rather seeing it maintain its value, being an accepted "currency" and store of value even if everything else became worthless.
There's another recent thread on stashing cash in the home - it's along similar lines. There are many reasons why it makes little sense to keep any significant amount of cash in the home. However, it is a hedge against the potential of something bad which may happen, whether that be your bank account gets looted, or electronic banking and the ATM system gets brought down by some ingenious hackers for some period of time. I'm comfortable with the $100 I walk around with in my wallet, while you can find others on that thread who have a couple thousand at home, to some who have buried wads of cash in various places on their property.
I personally do not have anything in commodities or precious metals. However, I do become more and more concerned about where things are headed with world economies and finances, and that financial/economic Armageddon has the potential of happening in my lifetime.