I can see how a person doing a large tank wants to save money. You can always hide the base rock. It's probably what I will do when I upgrade.
But more comes on live rock than bacteria. It has thousands of creatures that you can only get by going 'live'. To me, base makes no sense on small tanks (smaller than 100g, lets say).
One particular downside of dead rock is that it is an empty landscape, ready to be claimed. And the likely claimants are the fastest growers. Who are they? Unwanted algaes and other pests.
And don't get me started on manufactured rock.