What is the difference between Posting Edit Codes N and I as it pertains to Reports (both custom and

I cannot find a definite answer to this question: 

I thought that "N" should be used for all Header/Title Accounts and that a PEC of N would always appear on reports.

I thought that "I" should be used for all accounts that were once posting, but are now non-posting for whatever reason and that a PEC of I would not appear on reports if it had no balance.

How does Zero Row Suppression work with these with these posting edit codes?  Is there a difference?  I thought that N's would always appear but I's would not when you use zero row suppression.