Lately I have been doing lot of SAP retrofits on SAP implementations for clients who already have SAP implemented in their organizations, or SAP implemented but not in line with their business processes and requirements. I have noticed a common trend where standard SAP functionality (IMG Configuration) is being modified to meet their requirements. However, this is against the standard SAP practice as it can lead to issues when new functionality is introduced or existing functionality enhanced.
My suggestion is to always leave standard IMG settings as is, and always make a copy of it starting the name with Z or 9 for numbers (condition tables, etc.) and make necessary changes as required. This will help in comparing to standard settings and also gives the flexibility to make changes as required to achieve the requested functionality.
When we work with clients to resolve issues that arise when new functionality is introduced, we find that 99% of the time, the issues occur because standard SAP settings were changed.
Some situations require standard settings to be changed as they are hard coded in programs (ex: Delivery type for projects). My strong recommendation is to copy the standard settings to a Z version of it and then make required changes to the standard IMG settings. This will at least serve the purpose of standard settings if changes have to be reverted back at all.
So, rule of thumb is not to change SAP delivered IMG settings, and always make a copy of SAP delivered IMG settings and make necessary changes to the Z version. This will help in comparing standard settings and also will serve as a basis if changes have to be reverted back, or if you need to discard the Z version and use the SAP delivered settings.