Normal Balance

Hi,

I was adding a new program to my chart of accounts and realized that some of the "Normal Balances" on existing accounts were set up incorrectly (expense accounts were set up with "credit" as the normal balance). 

What is affected by the "Normal Balance?" Is this just an informational field? Or does it somehow affect reporting?

I just want to decide if I need to go back and review old financials or if I can just fix it and move on. 

Thanks in advance!