Flattening file before printing to maintain color accuracy

I just learned something new after many, many years of Photoshop use.

To make a long story short, I was experiencing maddening print color issues after switching to a new printer and paper and print profiles.  A lot of changes but when the dust settled, I still had crazy tints.  An example would be dark prints with heavy cyan casts.  But the error would change depending on the print in my catalog.

Oh no!  I thought I was faced with altering every image to look like my match prints from previous system.

I'll cut to the chase.  I learned that a file should be flattened before printing.  Not to save file size but to eliminate color casts.  The monitor image would look the same regardless but the print would be very different.  So, before pulling your hair out to get the prints to match the monitor, give flattening the image before printing a try.  I save my image with all the modification layers, etc.  I then select print and set up printer and color match dialogs but not print.  Then DONE and return to Photoshop and save.  Then flatten and return to print which will have all the settings.  (Be sure to not save  after flattening or you will, of course, lose all that critical layer info. 

I had never heard of this protocol until I received help from my printer model support tech.  He stated that printing with all layers often creates strange color casts.  Flattening fixed ALL my color match issues.

I am intererested in your experience and comments.