IDP certainly reduces costs. For instance, the IRS can process a digital tax return for $.35 vs. processing a paper tax return for $3. Also, IDP can scale and has a greater capacity to handle documents than humans do. When forms are processed faster, it saves costs associated with turnaround and time-to-market.
There are also the costs associated with manual errors. Where preventing an error costs $1, but correcting an error costs $10, and not correcting an error costs $100.