Advantages? #1...you have one run as your "control" (ie. it worked before) to measure/gauge/compare your "new" run with....they should match up....meaning "success!!!!!".
Disadvantages? Really?!?!? You "run with scissors"....your "new" run has issues/problems.....no one gets paid correctly....you don't find out till weeks later because you had nothing to really compare against.....and that is just the START!