Retesting Thoughts

This week has been focused on retesting and finally the time had come to retest.  However when the students originally took the tests they were given the tests in 2 seperate testing sessions but for retesting they had to do it all in one day.  My first thought was "Are you kidding me?", but then I thought maybe it is a good thing, get it done and over with today and the kids can start thinking about wrapping up the school year and start looking forward to moving onto the next grade.  This got me thinking that if we can do the retest in one day, then why are we seperating the original test into 2 days?  Is it an advantage or disadvantage?