My daughter was originally diagnosed as a non salt waster and after about a year of treatment (she began treatment at age 3) they added florinef to help her Cortef work better.  It worked.  She is now 17 and continues to take Florinef and will for life.  We were at the endo today (a new dr) and we were talking about this very thing.  He said it truly does help the Cortef to work better and sometimes you can actually decrease the Cortef.  While my daughter was diagnosed through lab work as a non salt waster, he said because she was very mildly virilized (no surgery required) she probably always lost a little salt all her life before being put on Florinef.  Now that she has taken it for 13 years, she has probably lost her ability to produce enough Aldosterone to retain the proper amount of salt and that is why she will be on it for life.  We did try (at another dr’s suggestion) to take her off it one time and the results were disastrous after 2 days.  She went back on it the 2nd evening, ate something very salty, and was just fine.   I know you have a son, but I hope this info helps.