One of the research projects I have done for “Microsoft Application Transporter 2006 for Lotus Domino” was the use of multiple instances. Multiple instances support is a great feature for this tool. It allows migration of several applications at the same time in order to gain in performance. In my test, I migrated copies of Lotus applications with 2000 records each to different WSS sites using 2, 3, and 5 instances of Application Transporter. The gain was calculated by comparing the migration time using multiple instances to the time that was necessary to migrate same amount of data using 1 instance.
The results were amazing! The performance gain varied depending on the number of documents in each Notes application, but in our tests, running multiple instances of Application Transporter was more efficient than running a single instance. You will always see a performance benefit when you run multiple instances, however I did not test more than 5 instances running simultaneously and I think that increasing this number, at some point, may slow down the performance due to machine resources limitations.