The illustration is self-explanatory. While it is true that the production of small lots direct mail pieces is labor intensive, the cost pales in comparison to a large quantity direct mail run.
The direct mail 'short run' allows advertisers to test the waters and see what works before commiting to a large, costly direct mail production run.
DONMAC ideas! can develop both a short lot, test run direct mail program and then call upon the services of a large scale producer for a full-blown run.