Posting controls for pre-posting never show up in the transaction analysis because they are almost an addition. These are for enabling additional code parts (e.g. cost centre etc.) to be driven based on manual entry, but the retrieval for the account will still be based on a different posting control - hence they don’t show as used.

If you remove the posting controls, this will take away the ability to pre-post the PO. This will only cause errors if the code part you are pre-posting is mandatory for the accounts used (and it will be missing now). 

Pre-accounting on POs etc. can be set to mandatory or optional - if they are currently set to mandatory, then removing them will affect users when they enter POs, as they will no longer be prompted to perform the pre-posting. 

To understand if they are necessary, I’d look at the code part used in pre-posting (e.g. cost centre) and then check the PO postings where this code part is filled out. If there are none - it’s probably safe to remove. If there are transactions with the code part filled - I’d leave the posting controls in.

Thank you @Ieva Rituma.  This information is greatly appreciated.

This is exactly what I needed.