I'm not a scientist nor a lab technician, but the internal medicine department in my med school insisted that we do our own lab work for our patient reports, which include the use of centrifuge for urinalysis.
To this day i'm still amazed at how many of my friends didn't actually understand that the tube of water is for counterbalance and not some magic to make their result better. Some of them thought that what's important is to add a tube of water and the placement is less important, which resulted in the centrifuge being run with two tubes side by side without anything on the opposite end.